W. R. Berkley (WRB) 10-Q3 May 242024 Q1 Quarterly reportFinancial data

Company Profile

Cover Page

Cover Page - shares	3 Months Ended
Cover Page - shares	Mar. 31, 2024	Apr. 29, 2024
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	1-15202
Entity Registrant Name	W. R. BERKLEY CORP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-1867895
Entity Address, Address Line One	475 Steamboat Road
Entity Address, City or Town	Greenwich
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06830
City Area Code	(203)
Local Phone Number	629-3000
Title of 12(b) Security	Common Stock, par value $.20 per share
Trading Symbol	WRB
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		255,662,277
Entity Central Index Key	0000011544
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
5.700% Subordinated Debentures due 2058
Entity Information [Line Items]
Title of 12(b) Security	5.700% Subordinated Debentures due 2058
Trading Symbol	WRB-PE
Security Exchange Name	NYSE
5.100% Subordinated Debentures due 2059
Entity Information [Line Items]
Title of 12(b) Security	5.100% Subordinated Debentures due 2059
Trading Symbol	WRB-PF
Security Exchange Name	NYSE
4.250% Subordinated Debentures due 2060
Entity Information [Line Items]
Title of 12(b) Security	4.250% Subordinated Debentures due 2060
Trading Symbol	WRB-PG
Security Exchange Name	NYSE
4.125% Subordinated Debentures due 2061
Entity Information [Line Items]
Title of 12(b) Security	4.125% Subordinated Debentures due 2061
Trading Symbol	WRB-PH
Security Exchange Name	NYSE

Consolidated Balance Sheets Con

Consolidated Balance Sheets Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investments:
Fixed maturity securities (amortized cost of $21,775,516 and $20,915,245; allowance for expected credit losses of $22,869 and $36,751 at March 31, 2024 and December 31, 2023, respectively)	$ 20,964,854	$ 20,178,308
Investment funds	1,555,818	1,621,655
Real estate	1,273,063	1,249,874
Equity securities	1,178,048	1,090,347
Arbitrage trading account	1,146,119	938,049
Loans receivable (net of allowance for expected credit losses of $2,609 and $3,004 at March 31, 2024 and December 31, 2023, respectively)	228,766	201,271
Total investments	26,346,668	25,279,504
Cash and cash equivalents	1,169,053	1,363,195
Premiums and fees receivable (net of allowance for expected credit losses of $35,039 and $35,110 at March 31, 2024 and December 31, 2023, respectively)	3,171,108	3,109,334
Due from reinsurers (net of allowance for expected credit losses of $9,185 and $8,404 at March 31, 2024 and December 31, 2023, respectively)	3,510,097	3,534,527
Deferred policy acquisition costs	888,719	861,609
Prepaid reinsurance premiums	757,659	758,927
Trading account receivables from brokers and clearing organizations	141,277	303,614
Property, furniture and equipment	466,855	426,803
Goodwill	174,597	174,597
Accrued investment income	217,801	213,408
Current and deferred federal and foreign income taxes	120,754	220,756
Other assets	886,484	865,556
Total assets	37,851,072	37,111,830
Liabilities:
Reserves for losses and loss expenses	19,099,628	18,739,652
Unearned premiums	5,996,812	5,922,326
Due to reinsurers	683,508	631,164
Trading account securities sold but not yet purchased	40,298	9,357
Other liabilities	1,395,048	1,503,053
Senior notes and other debt	1,827,997	1,827,951
Subordinated debentures	1,009,269	1,009,090
Total liabilities	30,052,560	29,642,593
Equity:
Perferred stock, par value $.10 per share: Authorized 5,000,000 shares; issued and outstanding - none	0	0
Common stock, par value $.20 per share: Authorized 500,000,000 shares, issued and outstanding, net of treasury shares, 177,930,502 and 183,411,907 shares, respectively	105,803	105,803
Additional paid-in capital	1,030,475	1,017,691
Retained earnings	11,455,158	11,040,908
Accumulated other comprehensive loss	(1,023,530)	(925,838)
Treasury stock, at cost, 272,465,959 and 272,469,871 shares, respectively	(3,783,074)	(3,783,133)
Total stockholders’ equity	7,784,832	7,455,431
Noncontrolling interests	13,680	13,806
Total equity	7,798,512	7,469,237
Total liabilities and equity	$ 37,851,072	$ 37,111,830

Consolidated Balance Sheets C_2

Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Fixed maturity securities, amortized cost	$ 21,775,516	$ 20,915,245
Fixed maturity securities, allowance for credit loss	22,869	36,751
Cumulative effect adjustment resulting from changes in accounting principles	2,609	3,004
Cumulative effect adjustment resulting from changes in accounting principles	35,039	35,110
Reinsurance recoverable, allowance for credit loss	$ 9,185	$ 8,404
Preferred stock, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred stock issued (in shares)	5,000,000	5,000,000
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollar per share)	$ 0.20	$ 0.20
Common shares authorized (in shares)		1,250,000,000
Common shares issued (in shares)	256,548,669	256,544,757
Common shares outstanding (in shares)	256,548,669	256,544,757
Treasury stock issued at cost (in shares)	272,465,959	272,469,871

Consolidated Statements Income

Consolidated Statements Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
REVENUES:
Net premiums written	$ 2,851,291	$ 2,574,824
Change in net unearned premiums	(86,944)	(83,392)
Net premiums earned	2,764,347	2,491,432
Net investment income	319,839	223,398
Net realized and unrealized gains on investments	11,503	22,611
Change in allowance for expected credit losses on investments	14,277	399
Net investment gains	25,780	23,010
Revenues from non-insurance businesses	120,992	124,200
Insurance service fees	25,319	32,857
Other income	496	107
Total revenues	3,256,773	2,895,004
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	1,663,778	1,538,755
Other operating costs and expenses	868,589	825,575
Expenses from non-insurance businesses	118,607	122,767
Interest expense	31,728	31,836
Total operating costs and expenses	2,682,702	2,518,933
Income before income taxes	574,071	376,071
Income tax expense	(132,036)	(80,342)
Net income before noncontrolling interests	442,035	295,729
Noncontrolling interests	436	(1,603)
Net income to common stockholders	$ 442,471	$ 294,126
NET INCOME PER SHARE:
Basic (in dollar per share)	$ 1.65	$ 1.07
Diluted (in dollar per share)	$ 1.64	$ 1.06

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income before noncontrolling interests	$ 442,035	$ 295,729
Other comprehensive (loss) income:
Change in unrealized currency translation adjustments	(27,570)	4,866
Change in unrealized investment (losses) gains, net of taxes	(70,122)	180,799
Other comprehensive (loss) income	(97,692)	185,665
Comprehensive income	344,343	481,394
Noncontrolling interests	436	(1,602)
Comprehensive income to common stockholders	$ 344,779	$ 479,792

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated Other Comprehensive Income (Loss)	Unrealized investment gain	Currency Translation Adjustments	Treasury stock	Noncontrolling interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment resulting from changes in accounting principles		$ 105,803	$ 997,534	$ 10,161,005	$ (1,264,581)	$ (892,905)	$ (371,676)	$ (3,251,429)	$ 19,829
Beginning of period at Dec. 31, 2022		105,803	997,534	10,161,005	(1,264,581)	(892,905)	(371,676)	(3,251,429)	19,829
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(1,200)
Restricted stock units expensed			11,794
Net income before noncontrolling interests	$ 295,729			294,126					1,603
Dividends ($0.11 and $0.60 per share, respectively)				(158,592)
Change in unrealized (losses) gains on securities without an allowance for expected credit losses	180,799					177,342
Change in unrealized gains on securities with an allowance for expected credit losses						3,456
Net change in period	4,866						4,866
Stock exercised/vested								395
Stock repurchased								(135,152)
Other	(1,352)
Contributions									177
Other comprehensive loss, net of tax	$ 185,665				185,665		4,866		(1)
End of period at Mar. 31, 2023			1,008,128	10,296,539	(1,078,917)	(712,107)	(366,810)	(3,387,538)	21,608
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.60
Cumulative effect adjustment resulting from changes in accounting principles			1,008,128	10,296,539	(1,078,917)	(712,107)	(366,810)	(3,387,538)	21,608
Cumulative effect adjustment resulting from changes in accounting principles	$ 7,469,237	105,803	1,017,691	11,040,908	(925,838)	(586,354)	(339,484)	(3,783,133)	13,806
Beginning of period at Dec. 31, 2023	7,469,237	$ 105,803	1,017,691	11,040,908	(925,838)	(586,354)	(339,484)	(3,783,133)	13,806
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock units issued			(195)
Restricted stock units expensed			12,979
Net income before noncontrolling interests	442,035			442,471					(436)
Dividends ($0.11 and $0.60 per share, respectively)				(28,221)
Change in unrealized (losses) gains on securities without an allowance for expected credit losses	(70,122)					(71,109)
Change in unrealized gains on securities with an allowance for expected credit losses						987
Net change in period	(27,570)						(27,570)
Stock exercised/vested								59
Stock repurchased								0
Other	0
Contributions									310
Other comprehensive loss, net of tax	(97,692)				(97,692)		(27,570)		0
End of period at Mar. 31, 2024	$ 7,798,512		1,030,475	11,455,158	(1,023,530)	(656,476)	(367,054)	(3,783,074)	13,680
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock dividends, per share, cash paid (in dollars per share)	$ 0.11
Cumulative effect adjustment resulting from changes in accounting principles	$ 7,798,512		$ 1,030,475	$ 11,455,158	$ (1,023,530)	$ (656,476)	$ (367,054)	$ (3,783,074)	$ 13,680

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
CASH FROM OPERATING ACTIVITIES:
Net income to common stockholders	$ 442,471	$ 294,126
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(25,780)	(23,010)
Depreciation and (accretion) amortization	(80,784)	9,737
Noncontrolling interests	(436)	1,603
Investment funds	29,349	(2,180)
Stock incentive plans	12,979	11,793
Change in:
Arbitrage trading account	(14,793)	(14,879)
Premiums and fees receivable	(68,133)	(33,460)
Reinsurance accounts	81,684	(84,746)
Deferred policy acquisition costs	(28,283)	(23,727)
Income taxes	120,052	76,933
Reserves for losses and loss expenses	393,176	424,149
Unearned premiums	84,952	87,991
Other	(200,219)	(279,007)
Net cash from operating activities	746,235	445,323
CASH USED IN INVESTING ACTIVITIES:
Proceeds from sale of fixed maturity securities	426,084	429,400
Proceeds from sale of equity securities	83,987	9,933
Distributions from investment funds	31,238	7,518
Proceeds from maturities and prepayments of fixed maturity securities	968,330	956,308
Purchase of fixed maturity securities	(2,266,087)	(1,686,107)
Purchase of equity securities	(105,599)	(59,529)
Real estate (purchased) sold	(30,697)	7,472
Change in loans receivable	(28,150)	612
Net purchases of property, furniture and equipment	(54,335)	(11,532)
Change in balances due to security brokers	70,120	(13,598)
Other	0	93
Net cash used in investing activities	(905,109)	(359,430)
CASH USED IN FINANCING ACTIVITIES:
Net proceeds (payments) from issuance of debt	20	(868)
Cash dividends to common stockholders	(28,220)	(158,592)
Purchase of common treasury shares	0	(135,152)
Other, net	(1,505)	(1,114)
Net cash used in financing activities	(29,705)	(295,726)
Net impact on cash due to change in foreign exchange rates	(5,563)	2,844
Net change in cash and cash equivalents	(194,142)	(206,989)
Cash and cash equivalents at beginning of period	1,363,195	1,449,346
Cash and cash equivalents at end of period	$ 1,169,053	$ 1,242,357

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive (Loss) Income	3 Months Ended
Consolidated Statements of Comprehensive (Loss) Income	Mar. 31, 2024
Equity [Abstract]
Consolidated Statements of Comprehensive (Loss) Income	Consolidated Statements of Comprehensive (Loss) Income The following table presents the components of the changes in accumulated other comprehensive (loss) income ("AOCI"): (In thousands) Unrealized Investment (Losses) Gains Currency Translation Adjustments Accumulated Other Comprehensive As of and for the three months ended March 31, 2024 Changes in AOCI Beginning of period $ (586,354) $ (339,484) $ (925,838) Other comprehensive loss before reclassifications (101,312) (27,570) (128,882) Amounts reclassified from AOCI 31,190 — 31,190 Other comprehensive loss (70,122) (27,570) (97,692) Unrealized investment loss related to noncontrolling interest — — — End of period $ (656,476) $ (367,054) $ (1,023,530) Amounts reclassified from AOCI Pre-tax $ 39,481 (1) $ — $ 39,481 Tax effect (8,291) (2) — (8,291) After-tax amounts reclassified $ 31,190 $ — $ 31,190 Other comprehensive loss Pre-tax $ (89,297) $ (27,570) $ (116,867) Tax effect 19,175 — 19,175 Other comprehensive loss $ (70,122) $ (27,570) $ (97,692) As of and for the three months ended March 31, 2023 Changes in AOCI Beginning of period $ (892,905) $ (371,676) $ (1,264,581) Other comprehensive income before reclassifications 155,215 4,866 160,081 Amounts reclassified from AOCI 25,584 — 25,584 Other comprehensive income 180,799 4,866 185,665 Unrealized investment loss related to noncontrolling interest (1) — (1) Ending balance $ (712,107) $ (366,810) $ (1,078,917) Amounts reclassified from AOCI Pre-tax $ 32,385 (1) $ — $ 32,385 Tax effect (6,801) (2) — (6,801) After-tax amounts reclassified $ 25,584 $ — $ 25,584 Other comprehensive income Pre-tax $ 232,021 $ 4,866 $ 236,887 Tax effect (51,222) — (51,222) Other comprehensive income $ 180,799 $ 4,866 $ 185,665 ____________ (1) Net investment gains in the consolidated statements of income. (2) Income tax expense in the consolidated statements of income.

Statements of Cash Flows

Statements of Cash Flows	3 Months Ended
Statements of Cash Flows	Mar. 31, 2024
Supplemental Cash Flow Elements [Abstract]
Statements of Cash Flows	Statements of Cash Flows Interest payments were $28,577,000 and $41,150,000 for the three months ended March 31, 2024 and 2023, respectively. There were no income taxes paid for the three months ended March 31, 2024 and 2023, respectively.

General

General	3 Months Ended
General	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	General The unaudited consolidated financial statements, which include the accounts of W. R. Berkley Corporation and its subsidiaries (the “Company”), have been prepared on the basis of U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all the information and notes required by GAAP for annual financial statements. The unaudited consolidated financial statements reflect all adjustments, consisting only of normal recurring items, which are necessary to present fairly the Company’s financial position and results of operations on a basis consistent with the prior audited consolidated financial statements. Operating results for interim periods are not necessarily indicative of the results that may be expected for the year. All significant intercompany accounts and transactions have been eliminated. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the revenues and expenses reflected during the reporting period. For further information related to areas of judgment and estimates and other information necessary to understand the Company’s financial position and results of operations, refer to the audited consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. Reclassifications have been made in the 2023 financial statements as originally reported to conform to the presentation of the 2024 financial statements. The Company reclassified a program management business from the Insurance segment to the Reinsurance & Monoline Excess segment. The reclassified business is a program management business offering support on a nationwide basis for commercial casualty and property program administrators.

Per Share Data

Per Share Data	3 Months Ended
Per Share Data	Mar. 31, 2024
Earnings Per Share [Abstract]
Per Share Data	Per Share Data The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period (including 11,663,450 and 11,416,856 common shares held in a grantor trust as of March 31, 2024 and 2023, respectively). The common shares held in the grantor trust are for delivery upon settlement of vested but mandatorily deferred restricted stock units ("RSUs"). Shares held by the grantor trust do not affect diluted shares outstanding since the shares deliverable under vested RSUs were already included in diluted shares outstanding. Diluted EPS is based upon the weighted average number of basic and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows: For the Three Months (In thousands) 2024 2023 Basic 268,211 274,977 Diluted 270,505 277,339

Recent Accounting Pronouncement

Recent Accounting Pronouncements and Accounting Policies	3 Months Ended
Recent Accounting Pronouncements and Accounting Policies	Mar. 31, 2024
Accounting Policies [Abstract]
Recent Accounting Pronouncements and Accounting Policies	Recent Accounting Pronouncements and Accounting Policies Recently adopted accounting pronouncements: All accounting and reporting standards that became effective in 2024 were either not applicable to the Company or their adoption did not have a material impact on the Company. Accounting and reporting standards that are not yet effective: All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

Investments In Fixed Maturity S

Investments In Fixed Maturity Securities	3 Months Ended
Investments In Fixed Maturity Securities	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Investments In Fixed Maturity Securities	Investments in Fixed Maturity Securities At March 31, 2024 and December 31, 2023, investments in fixed maturity securities were as follows: (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses March 31, 2024 Held to maturity: State and municipal $ 51,258 $ (38) $ 2,276 $ — $ 53,496 $ 51,220 Residential mortgage-backed 2,762 — 82 — 2,844 2,762 Total held to maturity 54,020 (38) 2,358 — 56,340 53,982 Available for sale: U.S. government and government agency 1,875,920 — 8,888 (55,256) 1,829,552 1,829,552 State and municipal: Special revenue 1,626,511 — 3,370 (83,769) 1,546,112 1,546,112 State general obligation 393,807 — 1,833 (16,316) 379,324 379,324 Pre-refunded 88,359 — 908 (214) 89,053 89,053 Corporate backed 166,261 (693) 539 (10,588) 155,519 155,519 Local general obligation 393,482 — 2,298 (13,002) 382,778 382,778 Total state and municipal 2,668,420 (693) 8,948 (123,889) 2,552,786 2,552,786 Mortgage-backed: Residential 1,963,060 — 9,805 (174,727) 1,798,138 1,798,138 Commercial 630,348 (562) 326 (20,232) 609,880 609,880 Total mortgage-backed 2,593,408 (562) 10,131 (194,959) 2,408,018 2,408,018 Asset-backed 4,298,768 (1,097) 6,475 (64,585) 4,239,561 4,239,561 Corporate: Industrial 3,865,664 — 14,741 (146,130) 3,734,275 3,734,275 Financial 3,172,945 — 10,100 (69,749) 3,113,296 3,113,296 Utilities 751,234 — 2,864 (24,436) 729,662 729,662 Other 590,644 — 2,516 (7,690) 585,470 585,470 Total corporate 8,380,487 — 30,221 (248,005) 8,162,703 8,162,703 Foreign government 1,904,493 (20,479) 8,585 (174,347) 1,718,252 1,718,252 Total available for sale 21,721,496 (22,831) 73,248 (861,041) 20,910,872 20,910,872 Total investments in fixed maturity securities $ 21,775,516 $ (22,869) $ 75,606 $ (861,041) $ 20,967,212 $ 20,964,854 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors. (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses December 31, 2023 Held to maturity: State and municipal $ 50,547 $ (43) $ 3,132 $ — $ 53,636 $ 50,504 Residential mortgage-backed 2,868 — 107 — 2,975 2,868 Total held to maturity 53,415 (43) 3,239 — 56,611 53,372 Available for sale: U.S. government and government agency 1,762,997 — 11,403 (57,669) 1,716,731 1,716,731 State and municipal: Special revenue 1,682,550 — 5,651 (82,006) 1,606,195 1,606,195 State general obligation 394,429 — 3,550 (16,405) 381,574 381,574 Pre-refunded 103,029 — 1,634 (185) 104,478 104,478 Corporate backed 166,873 (757) 696 (11,973) 154,839 154,839 Local general obligation 396,041 — 3,188 (11,893) 387,336 387,336 Total state and municipal 2,742,922 (757) 14,719 (122,462) 2,634,422 2,634,422 Mortgage-backed: Residential 1,773,206 — 12,780 (163,844) 1,622,142 1,622,142 Commercial 657,157 (158) 626 (13,312) 644,313 644,313 Total mortgage-backed 2,430,363 (158) 13,406 (177,156) 2,266,455 2,266,455 Asset-backed 4,252,883 (1,164) 8,527 (73,206) 4,187,040 4,187,040 Corporate: Industrial 3,679,219 (40) 24,312 (143,936) 3,559,555 3,559,555 Financial 2,838,220 (4,986) 14,681 (68,681) 2,779,234 2,779,234 Utilities 701,865 — 6,471 (23,412) 684,924 684,924 Other 635,975 — 1,605 (7,234) 630,346 630,346 Total corporate 7,855,279 (5,026) 47,069 (243,263) 7,654,059 7,654,059 Foreign government 1,817,386 (29,603) 15,865 (137,419) 1,666,229 1,666,229 Total available for sale 20,861,830 (36,708) 110,989 (811,175) 20,124,936 20,124,936 Total investments in fixed maturity securities $ 20,915,245 $ (36,751) $ 114,228 $ (811,175) $ 20,181,547 $ 20,178,308 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors. The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 43 $ 114 Provision for expected credit losses (5) (7) Allowance for expected credit losses, end of period $ 38 $ 107 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2024 and 2023: 2024 2023 (In thousands) Foreign Government Corporate Mortgage-backed Asset-backed State and Municipal Total Foreign Government Corporate Mortgage-backed Total Allowance for expected credit losses, beginning of period $ 29,603 $ 5,026 $ 158 $ 1,164 $ 757 $ 36,708 $ 32,633 $ 4,701 $ 18 $ 37,352 Expected credit losses on securities for which credit losses were not previously recorded — — 562 — — 562 — 186 — 186 Expected credit (gains) losses on securities for which credit losses were previously recorded (9,124) (5,026) (158) (67) (64) (14,439) 691 (1,087) 5 (391) Reduction due to disposals — — — — — — — (5) — (5) Allowance for expected credit losses, end of period $ 20,479 $ — $ 562 $ 1,097 $ 693 $ 22,831 $ 33,324 $ 3,795 $ 23 $ 37,142 During the three months ended March 31, 2024, the Company decreased the allowance for expected credit losses for available for sale securities utilizing its credit loss assessment process and inputs used in its credit loss model, primarily due to improved pricing associated with foreign government securities and corporate securities. During the three months ended March 31, 2023, the Company decreased the allowance for expected credit losses for available for sale securities utilizing its credit loss assessment process and inputs used in its credit loss model due to a decrease in unrealized losses primarily associated with corporate securities. The amortized cost and fair value of fixed maturity securities at March 31, 2024, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations. (In thousands) Amortized Fair Due in one year or less $ 1,980,563 $ 1,907,003 Due after one year through five years 9,877,133 9,528,047 Due after five years through ten years 4,681,226 4,577,859 Due after ten years 2,640,386 2,543,441 Mortgage-backed securities 2,596,170 2,410,862 Total $ 21,775,478 $ 20,967,212 ________________ (1) Amortized cost is reduced by the allowance for expected credit losses of $38 thousand related to held to maturity securities.

Investments in Equity Securitie

Investments in Equity Securities	3 Months Ended
Investments in Equity Securities	Mar. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Investments in Equity Securities	Investments in Fixed Maturity Securities At March 31, 2024 and December 31, 2023, investments in fixed maturity securities were as follows: (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses March 31, 2024 Held to maturity: State and municipal $ 51,258 $ (38) $ 2,276 $ — $ 53,496 $ 51,220 Residential mortgage-backed 2,762 — 82 — 2,844 2,762 Total held to maturity 54,020 (38) 2,358 — 56,340 53,982 Available for sale: U.S. government and government agency 1,875,920 — 8,888 (55,256) 1,829,552 1,829,552 State and municipal: Special revenue 1,626,511 — 3,370 (83,769) 1,546,112 1,546,112 State general obligation 393,807 — 1,833 (16,316) 379,324 379,324 Pre-refunded 88,359 — 908 (214) 89,053 89,053 Corporate backed 166,261 (693) 539 (10,588) 155,519 155,519 Local general obligation 393,482 — 2,298 (13,002) 382,778 382,778 Total state and municipal 2,668,420 (693) 8,948 (123,889) 2,552,786 2,552,786 Mortgage-backed: Residential 1,963,060 — 9,805 (174,727) 1,798,138 1,798,138 Commercial 630,348 (562) 326 (20,232) 609,880 609,880 Total mortgage-backed 2,593,408 (562) 10,131 (194,959) 2,408,018 2,408,018 Asset-backed 4,298,768 (1,097) 6,475 (64,585) 4,239,561 4,239,561 Corporate: Industrial 3,865,664 — 14,741 (146,130) 3,734,275 3,734,275 Financial 3,172,945 — 10,100 (69,749) 3,113,296 3,113,296 Utilities 751,234 — 2,864 (24,436) 729,662 729,662 Other 590,644 — 2,516 (7,690) 585,470 585,470 Total corporate 8,380,487 — 30,221 (248,005) 8,162,703 8,162,703 Foreign government 1,904,493 (20,479) 8,585 (174,347) 1,718,252 1,718,252 Total available for sale 21,721,496 (22,831) 73,248 (861,041) 20,910,872 20,910,872 Total investments in fixed maturity securities $ 21,775,516 $ (22,869) $ 75,606 $ (861,041) $ 20,967,212 $ 20,964,854 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors. (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses December 31, 2023 Held to maturity: State and municipal $ 50,547 $ (43) $ 3,132 $ — $ 53,636 $ 50,504 Residential mortgage-backed 2,868 — 107 — 2,975 2,868 Total held to maturity 53,415 (43) 3,239 — 56,611 53,372 Available for sale: U.S. government and government agency 1,762,997 — 11,403 (57,669) 1,716,731 1,716,731 State and municipal: Special revenue 1,682,550 — 5,651 (82,006) 1,606,195 1,606,195 State general obligation 394,429 — 3,550 (16,405) 381,574 381,574 Pre-refunded 103,029 — 1,634 (185) 104,478 104,478 Corporate backed 166,873 (757) 696 (11,973) 154,839 154,839 Local general obligation 396,041 — 3,188 (11,893) 387,336 387,336 Total state and municipal 2,742,922 (757) 14,719 (122,462) 2,634,422 2,634,422 Mortgage-backed: Residential 1,773,206 — 12,780 (163,844) 1,622,142 1,622,142 Commercial 657,157 (158) 626 (13,312) 644,313 644,313 Total mortgage-backed 2,430,363 (158) 13,406 (177,156) 2,266,455 2,266,455 Asset-backed 4,252,883 (1,164) 8,527 (73,206) 4,187,040 4,187,040 Corporate: Industrial 3,679,219 (40) 24,312 (143,936) 3,559,555 3,559,555 Financial 2,838,220 (4,986) 14,681 (68,681) 2,779,234 2,779,234 Utilities 701,865 — 6,471 (23,412) 684,924 684,924 Other 635,975 — 1,605 (7,234) 630,346 630,346 Total corporate 7,855,279 (5,026) 47,069 (243,263) 7,654,059 7,654,059 Foreign government 1,817,386 (29,603) 15,865 (137,419) 1,666,229 1,666,229 Total available for sale 20,861,830 (36,708) 110,989 (811,175) 20,124,936 20,124,936 Total investments in fixed maturity securities $ 20,915,245 $ (36,751) $ 114,228 $ (811,175) $ 20,181,547 $ 20,178,308 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors. The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 43 $ 114 Provision for expected credit losses (5) (7) Allowance for expected credit losses, end of period $ 38 $ 107 The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2024 and 2023: 2024 2023 (In thousands) Foreign Government Corporate Mortgage-backed Asset-backed State and Municipal Total Foreign Government Corporate Mortgage-backed Total Allowance for expected credit losses, beginning of period $ 29,603 $ 5,026 $ 158 $ 1,164 $ 757 $ 36,708 $ 32,633 $ 4,701 $ 18 $ 37,352 Expected credit losses on securities for which credit losses were not previously recorded — — 562 — — 562 — 186 — 186 Expected credit (gains) losses on securities for which credit losses were previously recorded (9,124) (5,026) (158) (67) (64) (14,439) 691 (1,087) 5 (391) Reduction due to disposals — — — — — — — (5) — (5) Allowance for expected credit losses, end of period $ 20,479 $ — $ 562 $ 1,097 $ 693 $ 22,831 $ 33,324 $ 3,795 $ 23 $ 37,142 During the three months ended March 31, 2024, the Company decreased the allowance for expected credit losses for available for sale securities utilizing its credit loss assessment process and inputs used in its credit loss model, primarily due to improved pricing associated with foreign government securities and corporate securities. During the three months ended March 31, 2023, the Company decreased the allowance for expected credit losses for available for sale securities utilizing its credit loss assessment process and inputs used in its credit loss model due to a decrease in unrealized losses primarily associated with corporate securities. The amortized cost and fair value of fixed maturity securities at March 31, 2024, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations. (In thousands) Amortized Fair Due in one year or less $ 1,980,563 $ 1,907,003 Due after one year through five years 9,877,133 9,528,047 Due after five years through ten years 4,681,226 4,577,859 Due after ten years 2,640,386 2,543,441 Mortgage-backed securities 2,596,170 2,410,862 Total $ 21,775,478 $ 20,967,212 ________________ (1) Amortized cost is reduced by the allowance for expected credit losses of $38 thousand related to held to maturity securities.
Equity securities
Debt Securities, Available-for-sale [Line Items]
Investments in Equity Securities	Investments in Equity Securities At March 31, 2024 and December 31, 2023, investments in equity securities were as follows: (In thousands) Cost Gross Unrealized Fair Carrying Gains Losses March 31, 2024 Common stocks $ 671,958 $ 196,093 $ (21,382) $ 846,669 $ 846,669 Preferred stocks 339,263 8,491 (16,375) 331,379 331,379 Total $ 1,011,221 $ 204,584 $ (37,757) $ 1,178,048 $ 1,178,048 December 31, 2023 Common stocks $ 664,997 $ 191,806 $ (18,749) $ 838,054 $ 838,054 Preferred stocks 284,335 3,075 (35,117) 252,293 252,293 Total $ 949,332 $ 194,881 $ (53,866) $ 1,090,347 $ 1,090,347

Arbitrage Trading Account

Arbitrage Trading Account	3 Months Ended
Arbitrage Trading Account	Mar. 31, 2024
Debt Securities, Trading, and Equity Securities, FV-NI [Abstract]
Arbitrage Trading Account	Arbitrage Trading Account At March 31, 2024 and December 31, 2023, the fair and carrying values of the arbitrage trading account were $1,146 million and $938 million, respectively. The primary focus of the trading account is merger arbitrage. Merger arbitrage is the business of investing in the securities of publicly held companies which are the targets in announced tender offers and mergers. Arbitrage investing differs from other types of investing in its focus on transactions and events believed likely to bring about a change in value over a relatively short time period (usually four months or less). The Company uses put options and call options in order to mitigate the impact of potential changes in market conditions on the merger arbitrage trading account. These options are reported at fair value. As of March 31, 2024, the fair value of long option contracts outstanding was $117 thousand (notional amount of $162 million) and the fair value of short option contracts was $40 million (notional amount of $162 million). Other than with respect to the use of these trading account securities, the Company does not make use of derivatives.

Net Investment Income

Net Investment Income	3 Months Ended
Net Investment Income	Mar. 31, 2024
Net Investment Income [Abstract]
Net Investment Income	Net Investment Income Net investment income consisted of the following: For the Three Months (In thousands) 2024 2023 Investment income (loss) earned on: Fixed maturity securities, including cash and cash equivalents and loans receivable $ 335,248 $ 195,642 Arbitrage trading account (1) 18,011 18,256 Equity securities 11,336 13,746 Investment funds (29,349) 2,180 Real estate (13,163) (3,711) Gross investment income 322,083 226,113 Investment expense (2,244) (2,715) Net investment income $ 319,839 $ 223,398

Investment Funds

Investment Funds	3 Months Ended
Investment Funds	Mar. 31, 2024
Equity Method Investments and Joint Ventures [Abstract]
Investment Funds	Investment Funds The Company evaluates whether it is an investor in a variable interest entity ("VIE"). Such entities do not have sufficient equity at risk to finance their activities without additional subordinated financial support, or the equity investors, as a group, do not have the characteristics of a controlling financial interest (primary beneficiary). The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE's capital structure, contractual terms, nature of the VIE's operations and purpose, and the Company's relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE and on an ongoing basis. The Company is not the primary beneficiary in any of its investment funds, and accordingly, carries its interests in investment funds under the equity method of accounting. The Company’s maximum exposure to loss with respect to these investments is limited to the carrying amount reported on the Company’s consolidated balance sheet and its unfunded commitments, which were $309 million as of March 31, 2024. Investment funds consisted of the following: Carrying Value as of Income (Loss) from March 31, December 31, For the Three Months (In thousands) 2024 2023 2024 2023 Financial services $ 418,877 $ 433,407 $ (13,491) $ (13,047) Transportation 296,021 344,278 (28,661) 11,788 Real Estate 189,309 201,625 5,356 956 Infrastructure 137,201 130,589 5,039 3,355 Energy 134,195 114,794 8,632 3,439 Other funds 380,215 396,962 (6,224) (4,311) Total $ 1,555,818 $ 1,621,655 $ (29,349) $ 2,180 The Company's share of the earnings or losses from investment funds is generally reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements. Financial services investment funds include the minority investment in Lifson Re, a Bermuda reinsurance company. Effective January 1, 2021, Lifson Re participated on a fully collateralized basis in a majority of the Company’s reinsurance placements for a 22.5% share of placed amounts. The percentage increased from 22.5% to 30.0% effective July 1, 2022. This pertains to all traditional reinsurance/retrocessional placements for both property and casualty business where there is more than one open market reinsurer participating. For the three months ended March 31, 2024 and 2023, the Company ceded approximately $94 million and $107 million, respectively, of written premiums to Lifson Re. Other funds include deferred compensation trust assets of $41 million and $36 million as of March 31, 2024 and December 31, 2023, respectively. These assets support other liabilities reflected in the balance sheet of an equal amount for employees who have elected to defer a portion of their compensation. The change in the net asset value of the trust is recorded in other funds within net investment income with an offsetting equal amount within corporate expenses.

Real Estate

Real Estate	3 Months Ended
Real Estate	Mar. 31, 2024
Real Estate [Abstract]
Real Estate	Real Estate Investment in real estate represents directly owned property held for investment, as follows: Carrying Value March 31, December 31, (In thousands) 2024 2023 Properties in operation $ 1,045,712 $ 1,022,654 Properties under development 227,351 227,220 Total $ 1,273,063 $ 1,249,874 As of March 31, 2024, properties in operation included a long-term ground lease in Washington, D.C., an office complex in New York City and the completed portion of a mixed-use project in Washington D.C. Properties in operation are net of accumulated depreciation and amortization of $34,131,000 and $32,745,000 as of March 31, 2024 and December 31, 2023, respectively. Related depreciation expense was $1,941,000 and $2,281,000 for the three months ended March 31, 2024 and 2023, respectively. Future minimum rental income expected on operating leases relating to properties in operation is $25,874,266 in 2024, $33,742,431 in 2025, $31,539,135 in 2026, $30,794,160 in 2027, $31,352,156 in 2028, $26,899,553 in 2029 and $413,976,622 thereafter.

Loans Receivable

Loans Receivable	3 Months Ended
Loans Receivable	Mar. 31, 2024
Receivables [Abstract]
Loans Receivable	Loans Receivable At March 31, 2024 and December 31, 2023, loans receivable were as follows: (In thousands) March 31, December 31, Amortized cost (net of allowance for expected credit losses): Real estate loans $ 227,431 $ 200,381 Commercial loans 1,335 890 Total $ 228,766 $ 201,271 Fair value: Real estate loans $ 227,821 $ 197,354 Commercial loans 1,335 890 Total $ 229,156 $ 198,244 The real estate loans are secured by commercial and residential real estate primarily located in the UK and New York. These loans generally earn interest at fixed or stepped interest rates and have maturities through 2026. The commercial loans are with small business owners who have secured the related financing with the assets of the business. Commercial loans primarily earn interest on a fixed basis and have varying maturities generally not exceeding 10 years. The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2024 and 2023: 2024 2023 (In thousands) Real Estate Loans Commercial Loans Total Real Estate Loans Commercial Loans Total Allowance for expected credit losses, beginning of period $ 2,983 $ 21 $ 3,004 $ 1,100 $ 691 $ 1,791 Change in expected credit losses (396) 1 (395) (61) (121) (182) Allowance for expected credit losses, end of period $ 2,587 $ 22 $ 2,609 $ 1,039 $ 570 $ 1,609 The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions.

Net Investment (Losses) Gains

Net Investment (Losses) Gains	3 Months Ended
Net Investment (Losses) Gains	Mar. 31, 2024
Realized and Unrealized Investment Gains (Losses) [Abstract]
Net Investment (Losses) Gains	Net Investment Gains Net investment gains were as follows: For the Three Months (In thousands) 2024 2023 Net investment gains: Fixed maturity securities: Gains $ 3,557 $ 943 Losses (2,323) (18,130) Equity securities (1): Net realized gains on investment sales 40,277 1,060 Change in unrealized gains 25,812 43,404 Investment funds 993 10 Real estate (2,216) 10,739 Loans receivable — — Other (2) (54,597) (15,415) Net realized and unrealized gains on investments in earnings before allowance for expected credit losses 11,503 22,611 Change in allowance for expected credit losses on investments: Fixed maturity securities 13,882 217 Loans receivable 395 182 Change in allowance for expected credit losses on investments 14,277 399 Net investment gains 25,780 23,010 Income tax expense (6,633) (4,850) After-tax net investment gains $ 19,147 $ 18,160 Change in unrealized investment (losses) gains on available for sale securities: Fixed maturity securities without allowance for expected credit losses $ (88,594) $ 227,116 Fixed maturity securities with allowance for expected credit losses 987 3,456 Investment funds (1,703) 1,936 Other 13 (487) Total change in unrealized investment (losses) gains (89,297) 232,021 Income tax benefit (expense) 19,175 (51,222) Noncontrolling interests — (1) After-tax change in unrealized investment (losses) gains of available for sale securities $ (70,122) $ 180,798 ______________________ (1) The net realized gains or losses on investment sales represent the total gains or losses from the purchase dates of the equity securities. The change in unrealized gains (losses) consists of two components: (i) the reversal of the gain or loss recognized in previous periods on equity securities sold and (ii) the change in unrealized gain or loss resulting from mark-to-market adjustments on equity securities still held.

Fixed Maturity Securities In An

Fixed Maturity Securities In An Unrealized Loss Position	3 Months Ended
Fixed Maturity Securities In An Unrealized Loss Position	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Fixed Maturity Securities In An Unrealized Loss Position	Fixed Maturity Securities in an Unrealized Loss Position The following tables summarize all fixed maturity securities in an unrealized loss position at March 31, 2024 and December 31, 2023 by the length of time those securities have been continuously in an unrealized loss position: Less Than 12 Months 12 Months or Greater Total (In thousands) Fair Gross Fair Gross Fair Gross March 31, 2024 U.S. government and government agency $ 439,699 $ 6,725 $ 666,947 $ 48,531 $ 1,106,646 $ 55,256 State and municipal 308,609 3,376 1,764,296 120,513 2,072,905 123,889 Mortgage-backed 288,696 5,023 1,374,227 189,936 1,662,923 194,959 Asset-backed 1,055,695 3,765 1,282,145 60,820 2,337,840 64,585 Corporate 1,532,300 16,754 4,372,753 231,251 5,905,053 248,005 Foreign government 321,236 5,078 754,322 169,269 1,075,558 174,347 Fixed maturity securities $ 3,946,235 $ 40,721 $ 10,214,690 $ 820,320 $ 14,160,925 $ 861,041 December 31, 2023 U.S. government and government agency $ 384,392 $ 6,655 $ 614,623 $ 51,014 $ 999,015 $ 57,669 State and municipal 264,273 3,013 1,680,034 119,449 1,944,307 122,462 Mortgage-backed 278,819 2,025 1,360,748 175,131 1,639,567 177,156 Asset-backed 413,511 2,070 2,176,035 71,136 2,589,546 73,206 Corporate 874,754 11,975 4,418,309 231,288 5,293,063 243,263 Foreign government 204,908 1,758 794,174 135,661 999,082 137,419 Fixed maturity securities $ 2,420,657 $ 27,496 $ 11,043,923 $ 783,679 $ 13,464,580 $ 811,175 Substantially all of the securities in an unrealized loss position are rated investment grade, except for the securities in the foreign government classification. A significant amount of the unrealized loss on foreign government securities is the result of changes in currency exchange rates. A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2024 is presented in the table below: ($ in thousands) Number of Aggregate Gross Foreign government 36 $ 93,212 $ 141,742 State and municipal 5 24,438 4,918 Corporate 25 42,772 2,291 Mortgage-backed 15 4,526 237 Asset-backed 4 86 70 Total 85 $ 165,034 $ 149,258 For fixed maturity securities that management does not intend to sell or to be required to sell, the portion of the decline in value that is considered to be due to credit factors is recognized in earnings, and the portion of the decline in value that is considered to be due to non-credit factors is recognized in other comprehensive income (loss).

Fair Value Measurements

Fair Value Measurements	3 Months Ended
Fair Value Measurements	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company’s fixed maturity available for sale securities, equity securities and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows: Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 - Quoted prices for similar assets or valuations based on inputs that are observable. Level 3 - Estimates of fair value based on internal pricing methodologies using unobservable inputs. Unobservable inputs are only used to measure fair value to the extent that observable inputs are not available. Substantially all of the Company’s fixed maturity securities were priced by independent pricing services. The prices provided by the independent pricing services are estimated based on observable market data in active markets utilizing pricing models and processes, which may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, sector groupings, matrix pricing and reference data. The pricing services may prioritize inputs differently on any given day for any security based on market conditions, and not all inputs are available for each security evaluation on any given day. The pricing services used by the Company have indicated that they will only produce an estimate of fair value if objectively verifiable information is available. The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness and periodically performs independent price tests of a sample of securities to ensure proper valuation. If prices from independent pricing services are not available for fixed maturity securities, the Company estimates the fair value. For Level 2 securities, the Company utilizes pricing models and processes which may include benchmark yields, sector groupings, matrix pricing, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, bids, offers and reference data. Where broker quotes are used, the Company generally requests two or more quotes and sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes received from brokers. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information. For Level 3 securities, the Company generally uses a discounted cash flow model to estimate the fair value of fixed maturity securities. The cash flow models are based upon assumptions as to prevailing credit spreads, interest rate and interest rate volatility, time to maturity and subordination levels. Projected cash flows are discounted at rates that are adjusted to reflect illiquidity, where appropriate. The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023 by level: (In thousands) Total Level 1 Level 2 Level 3 March 31, 2024 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 1,829,552 $ — $ 1,829,552 $ — State and municipal 2,552,786 — 2,552,786 — Mortgage-backed 2,408,018 — 2,408,018 — Asset-backed 4,239,561 — 4,239,561 — Corporate 8,162,703 — 8,162,703 — Foreign government 1,718,252 — 1,718,252 — Total fixed maturity securities available for sale 20,910,872 — 20,910,872 — Equity securities: Common stocks 846,669 843,441 1,059 2,169 Preferred stocks 331,379 — 327,743 3,636 Total equity securities 1,178,048 843,441 328,802 5,805 Arbitrage trading account 1,146,119 752,159 390,284 3,676 Total $ 23,235,039 $ 1,595,600 $ 21,629,958 $ 9,481 Liabilities: Trading account securities sold but not yet purchased $ 40,298 $ 40,298 $ — $ — December 31, 2023 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 1,716,731 $ — $ 1,716,731 $ — State and municipal 2,634,422 — 2,634,422 — Mortgage-backed 2,266,455 — 2,266,455 — Asset-backed 4,187,040 — 4,187,040 — Corporate 7,654,059 — 7,654,059 — Foreign government 1,666,229 — 1,666,229 — Total fixed maturity securities available for sale 20,124,936 — 20,124,936 — Equity securities: Common stocks 838,054 835,338 1,158 1,558 Preferred stocks 252,293 — 248,598 3,695 Total equity securities 1,090,347 835,338 249,756 5,253 Arbitrage trading account 938,049 546,110 388,167 3,772 Total $ 22,153,332 $ 1,381,448 $ 20,762,859 $ 9,025 Liabilities: Trading account securities sold but not yet purchased $ 9,357 $ 9,357 $ — $ — The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2024 and for the year ended December 31, 2023: Gains (Losses) Included In: (In thousands) Beginning Earnings (Losses) Other Impairments Purchases Sales Paydowns / Maturities Transfers In / (Out) Ending Three Months Ended March 31, 2024 Assets: Equity securities: Common stocks $ 1,558 $ 611 $ — $ — $ — $ — $ — $ — $ 2,169 Preferred stocks 3,695 (2) — — — (57) — — 3,636 Total 5,253 609 — — — (57) — — 5,805 Arbitrage trading account 3,772 (133) — — — — — 37 3,676 Total $ 9,025 $ 476 $ — $ — $ — $ (57) $ — $ 37 $ 9,481 Year Ended Assets: Equity securities: Common stocks $ 2,599 $ (1,041) $ — $ — $ — $ — $ — $ — $ 1,558 Preferred stocks 11,299 (3) — (7,601) — — — — 3,695 Total 13,898 (1,044) — (7,601) — — — — 5,253 Arbitrage trading account 3,590 117 — — — — — 65 3,772 Total $ 17,488 $ (927) $ — $ (7,601) $ — $ — $ — $ 65 $ 9,025 For the three months ended March 31, 2024 and for the year ended December 31, 2023, securities within the arbitrage trading account portfolio that no longer had a publicly traded price were transferred into Level 3. The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments: March 31, 2024 December 31, 2023 (In thousands) Carrying Value Fair Value Carrying Value Fair Value Assets: Fixed maturity securities $ 20,964,854 $ 20,967,212 $ 20,178,308 $ 20,181,547 Equity securities 1,178,048 1,178,048 1,090,347 1,090,347 Arbitrage trading account 1,146,119 1,146,119 938,049 938,049 Loans receivable 228,766 229,156 201,271 198,244 Cash and cash equivalents 1,169,053 1,169,053 1,363,195 1,363,195 Trading account receivables from brokers and clearing organizations 141,277 141,277 303,614 303,614 Due from broker — — 36,747 36,747 Liabilities: Due to broker 33,027 33,027 — — Trading account securities sold but not yet purchased 40,298 40,298 9,357 9,357 Senior notes and other debt 1,827,997 1,435,877 1,827,951 1,480,076 Subordinated debentures 1,009,269 893,358 1,009,090 929,598

Reserves for Loss and Loss Expe

Reserves for Loss and Loss Expenses	3 Months Ended
Reserves for Loss and Loss Expenses	Mar. 31, 2024
Insurance [Abstract]
Reserves for Loss and Loss Expenses	Reserves for Loss and Loss Expenses The Company's reserves for losses and loss expenses are comprised of case reserves and incurred but not reported liabilities ("IBNR"). When a claim is reported, a case reserve is established for the estimated ultimate payment based upon known information about the claim. As more information about the claim becomes available over time, case reserves are adjusted up or down as appropriate. Reserves are also established on an aggregate basis to provide for IBNR liabilities and expected loss reserve development on reported claims. Loss reserves included in the Company’s financial statements represent management’s best estimates based upon an actuarially derived point estimate and other considerations. The Company uses a variety of actuarial techniques and methods to derive an actuarial point estimate for each operating unit. These methods include paid loss development, incurred loss development, paid and incurred Bornhuetter-Ferguson methods and frequency and severity methods. In circumstances where one actuarial method is considered more credible than the others, that method is used to set the point estimate. The actuarial point estimate may also be based on a judgmental weighting of estimates produced from each of the methods considered. Industry loss experience is used to supplement the Company’s own data in selecting “tail factors” in areas where the Company’s own data is limited. The actuarial data is analyzed by line of business, coverage and accident or policy year, as appropriate, for each operating unit. The establishment of the actuarially derived loss reserve point estimate also includes consideration of qualitative factors that may affect the ultimate losses. These qualitative considerations include, among others, the impact of re-underwriting initiatives, changes in the mix of business, changes in distribution sources and changes in policy terms and conditions. The key assumptions used to arrive at the best estimate of loss reserves are the expected loss ratios, rate of loss cost inflation, and reported and paid loss emergence patterns. Expected loss ratios represent management’s expectation of losses at the time the business is priced and written, before any actual claims experience has emerged. This expectation is a significant determinant of the estimate of loss reserves for recently written business where there is little paid or incurred loss data to consider. Expected loss ratios are generally derived from historical loss ratios adjusted for the impact of rate changes, loss cost trends and known changes in the type of risks underwritten. Expected loss ratios are estimated for each key line of business within each operating unit. Expected loss cost inflation is particularly important for the long-tail lines, such as excess casualty, and claims with a high medical component, such as workers’ compensation. Reported and paid loss emergence patterns are used to project current reported or paid loss amounts to their ultimate settlement value. Loss development factors are based on the historical emergence patterns of paid and incurred losses, and are derived from the Company’s own experience and industry data. The paid loss emergence pattern is also significant to excess and assumed workers’ compensation reserves because those reserves are discounted to their estimated present value based upon such estimated payout patterns. Loss frequency and severity are measures of loss activity that are considered in determining the key assumptions described in our discussion of loss and loss expense reserves, including expected loss ratios, rate of loss cost inflation and reported and paid loss emergence patterns. Loss frequency is a measure of the number of claims per unit of insured exposure, and loss severity is a measure of the average size of claims. Factors affecting loss frequency include the effectiveness of loss controls and safety programs and changes in economic activity or weather patterns. Factors affecting loss severity include changes in policy limits, retentions, rate of inflation and judicial interpretations. Another factor affecting estimates of loss frequency and severity is the loss reporting lag, which is the period of time between the occurrence of a loss and the date the loss is reported to the Company. The length of the loss reporting lag affects our ability to accurately predict loss frequency (loss frequencies are more predictable for lines with short reporting lags) as well as the amount of reserves needed for incurred but not reported losses (less IBNR is required for lines with short reporting lags). As a result, loss reserves for lines with short reporting lags are likely to have less variation from initial loss estimates. For lines with short reporting lags, which include commercial automobile, primary workers’ compensation, other liability (claims-made) and property business, the key assumption is the loss emergence pattern used to project ultimate loss estimates from known losses paid or reported to date. For lines of business with long reporting lags, which include other liability (occurrence), products liability, excess workers’ compensation and liability reinsurance, the key assumption is the expected loss ratio since there is often little paid or incurred loss data to consider. Historically, the Company has experienced less variation from its initial loss estimates for lines of business with short reporting lags than for lines of business with long reporting lags. The key assumptions used in calculating the most recent estimate of the loss reserves are reviewed each quarter and adjusted, to the extent necessary, to reflect the latest reported loss data, current trends and other factors observed. The table below provides a reconciliation of the beginning and ending reserve balances: March 31, (In thousands) 2024 2023 Net reserves at beginning of period $ 15,661,820 $ 14,248,879 Net provision for losses and loss expenses: Claims occurring during the current year (1) 1,647,674 1,502,817 Increase in estimates for claims occurring in prior years (2) (3) 7,367 28,205 Loss reserve discount accretion 8,737 7,733 Total 1,663,778 1,538,755 Net payments for claims: Current year 107,434 110,274 Prior years 1,158,864 1,106,481 Total 1,266,298 1,216,755 Foreign currency translation (52,944) 1,154 Net reserves at end of period 16,006,356 14,572,033 Ceded reserves at end of period 3,093,272 2,859,602 Gross reserves at end of period $ 19,099,628 $ 17,431,635 _______________________________________ (1) Claims occurring during the current year are net of loss reserve discounts of $14 million and $11 million for the three months ended March 31, 2024 and 2023, respectively. (2) The change in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $10 million and increased by $19 million for the three months ended March 31, 2024 and 2023, respectively. (3) For certain retrospectively rated insurance policies and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable development, net of additional and return premiums, was $1 million and adverse development was $24 million for the three months ended March 31, 2024 and 2023, respectively. The ultimate net impact of COVID-19 on the Company’s reserves remains uncertain. As of March 31, 2024, the Company had recognized losses for COVID-19-related claims activity, net of reinsurance, of approximately $386 million, of which $328 million relates to the Insurance segment and $58 million relates to the Reinsurance & Monoline Excess segment. Such $386 million of COVID-19-related losses included $383 million of reported losses and $3 million of IBNR. During the three months ended March 31, 2024, favorable prior year development (net of additional and return premiums) of $1 million included $9 million for the Reinsurance & Monoline Excess segment largely offset by $8 million of adverse prior year development for the Insurance segment. For the Insurance segment, the adverse development during the first quarter of 2024 was driven by commercial auto liability and excess other liability, including umbrella, and was partially offset by favorable development for workers’ compensation and professional liability. The adverse commercial auto liability development was concentrated in accident years 2019 through 2023, while the excess other liability, including umbrella, development was focused in accident years 2017 through 2021. A significant portion of the excess other liability, including umbrella, development related to underlying commercial auto exposures. The Company believes that commercial auto-related claims are being particularly impacted by social inflation, which is contributing to an increase in the frequency of large losses beyond expectations. Social inflation can include higher settlement demands from plaintiffs, use of aggressive actions by the plaintiffs' bar such as litigation funding, negative public sentiment towards large businesses and corporations, and erosion of tort reforms, among others. The favorable workers’ compensation development for the Insurance segment was mainly related to accident years 2018 through 2023, while the favorable professional liability development was mainly in accident years 2021 and 2022. For workers’ compensation, favorable reported claim frequency, below expectations, continued to drive the favorable reserve development. For professional liability, the reported loss experience for the 2021 and 2022 accident years was better than expected. These accident years also feature business written at peak pricing levels, which the Company now believes will result in higher profitability than initially anticipated. For the Reinsurance & Monoline Excess segment, the favorable development was driven mainly by favorable development in excess workers’ compensation, partially offset by adverse development in the non-proportional reinsurance assumed liability line of business. The favorable excess workers’ compensation development was driven by continued lower claim frequency and reported losses relative to expectations, and to favorable claim settlements spread across many prior accident years. The unfavorable development for non-proportional reinsurance was concentrated mainly in accident years 2017 through 2019 and was associated primarily with our U.S. and U.K. excess general liability reinsurance businesses, including accounts reinsuring construction projects. During the three months ended March 31, 2023, adverse prior year development (net of additional and return premiums) of $24 million included $12 million for the Insurance segment and $12 million for the Reinsurance & Monoline Excess segment. This overall adverse development for both segments was primarily attributable to property catastrophe losses related to 2022 events which were still being adjusted and settled during the first quarter of 2023. In particular, losses related to U.S. winter storms which occurred during the month of December were a significant driver of the development, as information gathering and evaluation of many of these losses were still ongoing into 2023. In addition to the property prior year adverse development discussed above, during the first quarter of 2023, the Insurance segment experienced adverse prior year development on casualty lines for the 2016 through 2019 accident years, which was offset by favorable prior year development on casualty lines for the 2022 accident year. The adverse development on the 2016 through 2019 accident years was concentrated in the other liability line of business, and to a lesser degree, professional liability, including medical professional. The development, which particularly impacted business attaching excess of primary policy limits, was driven by a larger than expected number of large losses reported. The Company believes social inflation contributed to an increase in the frequency of large losses for these accident years. Social inflation can include higher settlement demands from plaintiffs, use of tactics such as litigation funding by the plaintiffs’ bar, negative public sentiment towards large businesses and corporations, and erosion of tort reforms, among others. The favorable prior year development on casualty lines for the 2022 accident year in the Insurance segment was concentrated in the other liability, professional liability, and workers’ compensation lines of business. Due to uncertainty regarding incurred loss frequency and severity in light of ongoing social inflation and the emergence from the COVID-19 pandemic, the Company set its initial loss ratios for the 2022 accident year prudently, and largely maintained these estimates through the end of 2022. The reported loss experience for these lines of business for the 2022 accident year was significantly better than expected, and the Company reacted to this favorable emergence in the first quarter of 2023.

Fair Value Of Financial Instrum

Fair Value Of Financial Instruments	3 Months Ended
Fair Value Of Financial Instruments	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Of Financial Instruments	Fair Value Measurements The Company’s fixed maturity available for sale securities, equity securities and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows: Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 - Quoted prices for similar assets or valuations based on inputs that are observable. Level 3 - Estimates of fair value based on internal pricing methodologies using unobservable inputs. Unobservable inputs are only used to measure fair value to the extent that observable inputs are not available. Substantially all of the Company’s fixed maturity securities were priced by independent pricing services. The prices provided by the independent pricing services are estimated based on observable market data in active markets utilizing pricing models and processes, which may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, sector groupings, matrix pricing and reference data. The pricing services may prioritize inputs differently on any given day for any security based on market conditions, and not all inputs are available for each security evaluation on any given day. The pricing services used by the Company have indicated that they will only produce an estimate of fair value if objectively verifiable information is available. The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness and periodically performs independent price tests of a sample of securities to ensure proper valuation. If prices from independent pricing services are not available for fixed maturity securities, the Company estimates the fair value. For Level 2 securities, the Company utilizes pricing models and processes which may include benchmark yields, sector groupings, matrix pricing, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, bids, offers and reference data. Where broker quotes are used, the Company generally requests two or more quotes and sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes received from brokers. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information. For Level 3 securities, the Company generally uses a discounted cash flow model to estimate the fair value of fixed maturity securities. The cash flow models are based upon assumptions as to prevailing credit spreads, interest rate and interest rate volatility, time to maturity and subordination levels. Projected cash flows are discounted at rates that are adjusted to reflect illiquidity, where appropriate. The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023 by level: (In thousands) Total Level 1 Level 2 Level 3 March 31, 2024 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 1,829,552 $ — $ 1,829,552 $ — State and municipal 2,552,786 — 2,552,786 — Mortgage-backed 2,408,018 — 2,408,018 — Asset-backed 4,239,561 — 4,239,561 — Corporate 8,162,703 — 8,162,703 — Foreign government 1,718,252 — 1,718,252 — Total fixed maturity securities available for sale 20,910,872 — 20,910,872 — Equity securities: Common stocks 846,669 843,441 1,059 2,169 Preferred stocks 331,379 — 327,743 3,636 Total equity securities 1,178,048 843,441 328,802 5,805 Arbitrage trading account 1,146,119 752,159 390,284 3,676 Total $ 23,235,039 $ 1,595,600 $ 21,629,958 $ 9,481 Liabilities: Trading account securities sold but not yet purchased $ 40,298 $ 40,298 $ — $ — December 31, 2023 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 1,716,731 $ — $ 1,716,731 $ — State and municipal 2,634,422 — 2,634,422 — Mortgage-backed 2,266,455 — 2,266,455 — Asset-backed 4,187,040 — 4,187,040 — Corporate 7,654,059 — 7,654,059 — Foreign government 1,666,229 — 1,666,229 — Total fixed maturity securities available for sale 20,124,936 — 20,124,936 — Equity securities: Common stocks 838,054 835,338 1,158 1,558 Preferred stocks 252,293 — 248,598 3,695 Total equity securities 1,090,347 835,338 249,756 5,253 Arbitrage trading account 938,049 546,110 388,167 3,772 Total $ 22,153,332 $ 1,381,448 $ 20,762,859 $ 9,025 Liabilities: Trading account securities sold but not yet purchased $ 9,357 $ 9,357 $ — $ — The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2024 and for the year ended December 31, 2023: Gains (Losses) Included In: (In thousands) Beginning Earnings (Losses) Other Impairments Purchases Sales Paydowns / Maturities Transfers In / (Out) Ending Three Months Ended March 31, 2024 Assets: Equity securities: Common stocks $ 1,558 $ 611 $ — $ — $ — $ — $ — $ — $ 2,169 Preferred stocks 3,695 (2) — — — (57) — — 3,636 Total 5,253 609 — — — (57) — — 5,805 Arbitrage trading account 3,772 (133) — — — — — 37 3,676 Total $ 9,025 $ 476 $ — $ — $ — $ (57) $ — $ 37 $ 9,481 Year Ended Assets: Equity securities: Common stocks $ 2,599 $ (1,041) $ — $ — $ — $ — $ — $ — $ 1,558 Preferred stocks 11,299 (3) — (7,601) — — — — 3,695 Total 13,898 (1,044) — (7,601) — — — — 5,253 Arbitrage trading account 3,590 117 — — — — — 65 3,772 Total $ 17,488 $ (927) $ — $ (7,601) $ — $ — $ — $ 65 $ 9,025 For the three months ended March 31, 2024 and for the year ended December 31, 2023, securities within the arbitrage trading account portfolio that no longer had a publicly traded price were transferred into Level 3. The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments: March 31, 2024 December 31, 2023 (In thousands) Carrying Value Fair Value Carrying Value Fair Value Assets: Fixed maturity securities $ 20,964,854 $ 20,967,212 $ 20,178,308 $ 20,181,547 Equity securities 1,178,048 1,178,048 1,090,347 1,090,347 Arbitrage trading account 1,146,119 1,146,119 938,049 938,049 Loans receivable 228,766 229,156 201,271 198,244 Cash and cash equivalents 1,169,053 1,169,053 1,363,195 1,363,195 Trading account receivables from brokers and clearing organizations 141,277 141,277 303,614 303,614 Due from broker — — 36,747 36,747 Liabilities: Due to broker 33,027 33,027 — — Trading account securities sold but not yet purchased 40,298 40,298 9,357 9,357 Senior notes and other debt 1,827,997 1,435,877 1,827,951 1,480,076 Subordinated debentures 1,009,269 893,358 1,009,090 929,598

Premiums and Reinsurance Relate

Premiums and Reinsurance Related Information	3 Months Ended
Premiums and Reinsurance Related Information	Mar. 31, 2024
Insurance [Abstract]
Premiums and Reinsurance Related Information	Premiums and Reinsurance Related Information The following is a summary of insurance and reinsurance financial information: For the Three Months (In thousands) 2024 2023 Written premiums: Direct $ 3,039,066 $ 2,738,754 Assumed 323,689 310,563 Ceded (511,464) (474,493) Total net premiums written $ 2,851,291 $ 2,574,824 Earned premiums: Direct $ 2,936,643 $ 2,667,063 Assumed 337,911 295,230 Ceded (510,207) (470,861) Total net premiums earned $ 2,764,347 $ 2,491,432 Ceded losses and loss expenses incurred $ 305,951 $ 315,476 Ceded commissions earned $ 121,054 $ 118,418 The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 35,110 $ 30,660 Change in expected credit losses (71) 1,693 Allowance for expected credit losses, end of period $ 35,039 $ 32,353 The Company reinsures a portion of its insurance exposures in order to reduce its net liability on individual risks and catastrophe losses. The Company also cedes premiums to state assigned risk plans and captive insurance companies. Estimated amounts due from reinsurers are reported net of an allowance for expected credit losses. The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 8,404 $ 8,064 Change in expected credit losses 781 639 Allowance for expected credit losses, end of period $ 9,185 $ 8,703

Restricted Stock Units

Restricted Stock Units	3 Months Ended
Restricted Stock Units	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Restricted Stock Units	Restricted Stock Units Pursuant to its stock incentive plan, the Company may issue restricted stock units ("RSUs") to employees of the Company and its subsidiaries. The RSUs generally vest three ($ in thousands) Units Fair Value 2024 1,214 $ 100 2023 — $ —

Litigation and Contingent Liabi

Litigation and Contingent Liabilities	3 Months Ended
Litigation and Contingent Liabilities	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Litigation and Contingent Liabilities	Litigation and Contingent Liabilities In the ordinary course of business, the Company is subject to disputes, litigation and arbitration arising from its insurance and reinsurance businesses. These matters are generally related to insurance and reinsurance claims and are considered in the establishment of loss and loss expense reserves. In addition, the Company may also become involved in legal actions which seek extra-contractual damages, punitive damages or penalties, including claims alleging bad faith in handling of insurance claims. The Company expects its ultimate liability with respect to such matters will not be material to its financial condition. However, adverse outcomes on such matters are possible, from time to time, and could be material to the Company’s results of operations in any particular financial reporting period. On December 22, 2023, one of the Company’s subsidiaries filed a lawsuit against certain reinsurers to recover in excess of $90 million in respect of certain losses paid to its policyholders under certain event cancellation and related insurance policies. The Company believes its claims against the reinsurers are meritorious and expects a positive resolution to its lawsuit. While an adverse outcome is possible, the Company believes that the outcome, in any case, will not be material to the Company’s financial condition.

Leases

Leases	3 Months Ended
Leases	Mar. 31, 2024
Leases [Abstract]
Leases	Leases Lessees are required to recognize a right-of-use asset and a lease liability for leases with terms of more than 12 months on the balance sheet. All leases disclosed within this footnote are classified as operating leases. Recognized right-of-use asset and lease liability are reported within other assets and other liabilities, respectively, in the consolidated balance sheet. Lease expense is reported in other operating costs and expenses in the consolidated statement of income and accounted for on a straight-line basis over the lease term. To determine the discount rate used to calculate present value of future minimum lease payments, the Company uses its incremental borrowing rate during the lease commencement period in line with the respective lease duration. In certain cases, the Company has the option to renew the lease. Lease renewal future payments are included in the present value of the future minimum lease payments when the Company determines it is reasonably certain to renew. The main leases entered into by the Company are for office space used by the Company’s operating units across the world. Additionally, the Company, to a lesser extent, has equipment leases mainly for office equipment. Further information relating to operating lease expense and other operating lease information are as follows: For the Three Months Ended (In thousands) 2024 2023 Leases: Lease cost $ 11,077 $ 10,188 Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows $ 12,232 $ 10,563 Right-of-use assets obtained in exchange for new lease liabilities $ 24,695 $ 5,313 As of March 31, ($ in thousands) 2024 2023 Right-of-use assets $ 191,720 $ 164,547 Lease liabilities $ 233,114 $ 199,225 Weighted-average remaining lease term 7.6 years 7.1 years Weighted-average discount rate 5.44 % 4.49 % Contractual maturities of the Company’s future minimum lease payments are as follows: (In thousands) March 31, 2024 Contractual Maturities: 2024 $ 38,862 2025 44,402 2026 37,499 2027 28,341 2028 26,760 Thereafter 104,223 Total undiscounted future minimum lease payments 280,087 Less: Discount impact 46,973 Total lease liability $ 233,114

Business Segments

Business Segments	3 Months Ended
Business Segments	Mar. 31, 2024
Segment Reporting [Abstract]
Business Segments	Business Segments The Company’s reportable segments include the following two business segments, plus a corporate segment: • Insurance - predominantly commercial insurance business, including excess and surplus lines, admitted lines and specialty personal lines throughout the United States, as well as insurance business in Asia, Australia, Canada, Continental Europe, Mexico, Scandinavia, South America and the United Kingdom. • Reinsurance & Monoline Excess - reinsurance business on a facultative and treaty basis, primarily in the United States, the United Kingdom, Continental Europe, Australia, the Asia-Pacific Region and South Africa, as well as operations that solely retain risk on an excess basis and certain program management business. The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Income tax expense and benefits are calculated based upon the Company's overall effective tax rate. Summary financial information about the Company's reporting segments is presented in the following tables. Income (loss) before income taxes by segment includes allocated investment income. Identifiable assets by segment are those assets used in or allocated to the operation of each segment. Revenues (In thousands) Earned Investment Other Total (2) Pre-Tax Income (Loss) Net Income (Loss) to Common Stockholders Three months ended March 31, 2024 Insurance $ 2,398,768 $ 244,778 $ 9,423 $ 2,652,969 $ 478,149 $ 365,091 Reinsurance & Monoline Excess 365,579 53,211 — 418,790 127,624 102,126 Corporate, other and eliminations (3) — 21,850 137,384 159,234 (57,482) (43,893) Net investment gains — — 25,780 25,780 25,780 19,147 Total $ 2,764,347 $ 319,839 $ 172,587 $ 3,256,773 $ 574,071 $ 442,471 Three months ended March 31, 2023 Insurance $ 2,142,924 $ 163,558 $ 9,577 $ 2,316,059 $ 352,626 $ 274,108 Reinsurance & Monoline Excess 348,508 54,583 — 403,091 101,285 82,357 Corporate, other and eliminations (3) — 5,257 147,587 152,844 (100,850) (80,499) Net investment gains — — 23,010 23,010 23,010 18,160 Total $ 2,491,432 $ 223,398 $ 180,174 $ 2,895,004 $ 376,071 $ 294,126 _________________ (1) Certain amounts included in earned premiums of each segment are related to inter-segment transactions. (2) Revenues for Insurance from foreign operations for the three months ended March 31, 2024 and 2023 were $393 million and $274 million, respectively. Revenues for Reinsurance & Monoline Excess from foreign operations for the three months ended March 31, 2024 and 2023 were $111 million and $106 million, respectively. (3) Corporate, other and eliminations represent corporate revenues and expenses that are not allocated to business segments. Identifiable Assets (In thousands) March 31, December 31, Insurance $ 30,048,006 $ 29,923,282 Reinsurance & Monoline Excess 5,506,533 5,545,249 Corporate, other and eliminations 2,296,533 1,643,299 Consolidated $ 37,851,072 $ 37,111,830 Net premiums earned by major line of business are as follows: For the Three Months (In thousands) 2024 2023 Insurance: Other liability $ 967,260 $ 853,472 Short-tail lines (1) 510,809 412,534 Auto 354,013 294,116 Workers' compensation 301,495 305,561 Professional liability 265,191 277,241 Total Insurance 2,398,768 2,142,924 Reinsurance & Monoline Excess: Casualty (2) 197,844 214,712 Property (2) 102,384 75,152 Monoline excess (3) 65,351 58,644 Total Reinsurance & Monoline Excess 365,579 348,508 Total $ 2,764,347 $ 2,491,432 ______________ (1) Short-tail lines include commercial multi-peril (non-liability), inland marine, accident and health, fidelity and surety, boiler and machinery, high net worth homeowners and other lines. (2) Includes reinsurance casualty and property and certain program management business.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss) to Common Stockholders	$ 442,471	$ 294,126

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements and Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Per Share Data	Per Share Data The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period (including 11,663,450 and 11,416,856 common shares held in a grantor trust as of March 31, 2024 and 2023, respectively). The common shares held in the grantor trust are for delivery upon settlement of vested but mandatorily deferred restricted stock units ("RSUs"). Shares held by the grantor trust do not affect diluted shares outstanding since the shares deliverable under vested RSUs were already included in diluted shares outstanding. Diluted EPS is based upon the weighted average number of basic and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows: For the Three Months (In thousands) 2024 2023 Basic 268,211 274,977 Diluted 270,505 277,339
Recent Accounting Pronouncements	Recent Accounting Pronouncements and Accounting Policies Recently adopted accounting pronouncements: All accounting and reporting standards that became effective in 2024 were either not applicable to the Company or their adoption did not have a material impact on the Company. Accounting and reporting standards that are not yet effective: All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

Consolidated Statements of Co_3

Consolidated Statements of Comprehensive (Loss) Income (Tables)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Components of changes in accumulated other comprehensive income (loss)	The following table presents the components of the changes in accumulated other comprehensive (loss) income ("AOCI"): (In thousands) Unrealized Investment (Losses) Gains Currency Translation Adjustments Accumulated Other Comprehensive As of and for the three months ended March 31, 2024 Changes in AOCI Beginning of period $ (586,354) $ (339,484) $ (925,838) Other comprehensive loss before reclassifications (101,312) (27,570) (128,882) Amounts reclassified from AOCI 31,190 — 31,190 Other comprehensive loss (70,122) (27,570) (97,692) Unrealized investment loss related to noncontrolling interest — — — End of period $ (656,476) $ (367,054) $ (1,023,530) Amounts reclassified from AOCI Pre-tax $ 39,481 (1) $ — $ 39,481 Tax effect (8,291) (2) — (8,291) After-tax amounts reclassified $ 31,190 $ — $ 31,190 Other comprehensive loss Pre-tax $ (89,297) $ (27,570) $ (116,867) Tax effect 19,175 — 19,175 Other comprehensive loss $ (70,122) $ (27,570) $ (97,692) As of and for the three months ended March 31, 2023 Changes in AOCI Beginning of period $ (892,905) $ (371,676) $ (1,264,581) Other comprehensive income before reclassifications 155,215 4,866 160,081 Amounts reclassified from AOCI 25,584 — 25,584 Other comprehensive income 180,799 4,866 185,665 Unrealized investment loss related to noncontrolling interest (1) — (1) Ending balance $ (712,107) $ (366,810) $ (1,078,917) Amounts reclassified from AOCI Pre-tax $ 32,385 (1) $ — $ 32,385 Tax effect (6,801) (2) — (6,801) After-tax amounts reclassified $ 25,584 $ — $ 25,584 Other comprehensive income Pre-tax $ 232,021 $ 4,866 $ 236,887 Tax effect (51,222) — (51,222) Other comprehensive income $ 180,799 $ 4,866 $ 185,665 ____________ (1) Net investment gains in the consolidated statements of income. (2) Income tax expense in the consolidated statements of income.

Per Share Data (Tables)

Per Share Data (Tables)	3 Months Ended
Per Share Data (Tables)	Mar. 31, 2024
Earnings Per Share [Abstract]
Weighted average number of common shares	The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows: For the Three Months (In thousands) 2024 2023 Basic 268,211 274,977 Diluted 270,505 277,339

Investments in Fixed Maturity_2

Investments in Fixed Maturity Securities (Tables)	3 Months Ended
Investments in Fixed Maturity Securities (Tables)	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Schedule of investments in fixed maturity securities	At March 31, 2024 and December 31, 2023, investments in fixed maturity securities were as follows: (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses March 31, 2024 Held to maturity: State and municipal $ 51,258 $ (38) $ 2,276 $ — $ 53,496 $ 51,220 Residential mortgage-backed 2,762 — 82 — 2,844 2,762 Total held to maturity 54,020 (38) 2,358 — 56,340 53,982 Available for sale: U.S. government and government agency 1,875,920 — 8,888 (55,256) 1,829,552 1,829,552 State and municipal: Special revenue 1,626,511 — 3,370 (83,769) 1,546,112 1,546,112 State general obligation 393,807 — 1,833 (16,316) 379,324 379,324 Pre-refunded 88,359 — 908 (214) 89,053 89,053 Corporate backed 166,261 (693) 539 (10,588) 155,519 155,519 Local general obligation 393,482 — 2,298 (13,002) 382,778 382,778 Total state and municipal 2,668,420 (693) 8,948 (123,889) 2,552,786 2,552,786 Mortgage-backed: Residential 1,963,060 — 9,805 (174,727) 1,798,138 1,798,138 Commercial 630,348 (562) 326 (20,232) 609,880 609,880 Total mortgage-backed 2,593,408 (562) 10,131 (194,959) 2,408,018 2,408,018 Asset-backed 4,298,768 (1,097) 6,475 (64,585) 4,239,561 4,239,561 Corporate: Industrial 3,865,664 — 14,741 (146,130) 3,734,275 3,734,275 Financial 3,172,945 — 10,100 (69,749) 3,113,296 3,113,296 Utilities 751,234 — 2,864 (24,436) 729,662 729,662 Other 590,644 — 2,516 (7,690) 585,470 585,470 Total corporate 8,380,487 — 30,221 (248,005) 8,162,703 8,162,703 Foreign government 1,904,493 (20,479) 8,585 (174,347) 1,718,252 1,718,252 Total available for sale 21,721,496 (22,831) 73,248 (861,041) 20,910,872 20,910,872 Total investments in fixed maturity securities $ 21,775,516 $ (22,869) $ 75,606 $ (861,041) $ 20,967,212 $ 20,964,854 ____________ (1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors. (In thousands) Amortized Allowance for Expected Credit Losses (1) Gross Unrealized Fair Carrying Gains Losses December 31, 2023 Held to maturity: State and municipal $ 50,547 $ (43) $ 3,132 $ — $ 53,636 $ 50,504 Residential mortgage-backed 2,868 — 107 — 2,975 2,868 Total held to maturity 53,415 (43) 3,239 — 56,611 53,372 Available for sale: U.S. government and government agency 1,762,997 — 11,403 (57,669) 1,716,731 1,716,731 State and municipal: Special revenue 1,682,550 — 5,651 (82,006) 1,606,195 1,606,195 State general obligation 394,429 — 3,550 (16,405) 381,574 381,574 Pre-refunded 103,029 — 1,634 (185) 104,478 104,478 Corporate backed 166,873 (757) 696 (11,973) 154,839 154,839 Local general obligation 396,041 — 3,188 (11,893) 387,336 387,336 Total state and municipal 2,742,922 (757) 14,719 (122,462) 2,634,422 2,634,422 Mortgage-backed: Residential 1,773,206 — 12,780 (163,844) 1,622,142 1,622,142 Commercial 657,157 (158) 626 (13,312) 644,313 644,313 Total mortgage-backed 2,430,363 (158) 13,406 (177,156) 2,266,455 2,266,455 Asset-backed 4,252,883 (1,164) 8,527 (73,206) 4,187,040 4,187,040 Corporate: Industrial 3,679,219 (40) 24,312 (143,936) 3,559,555 3,559,555 Financial 2,838,220 (4,986) 14,681 (68,681) 2,779,234 2,779,234 Utilities 701,865 — 6,471 (23,412) 684,924 684,924 Other 635,975 — 1,605 (7,234) 630,346 630,346 Total corporate 7,855,279 (5,026) 47,069 (243,263) 7,654,059 7,654,059 Foreign government 1,817,386 (29,603) 15,865 (137,419) 1,666,229 1,666,229 Total available for sale 20,861,830 (36,708) 110,989 (811,175) 20,124,936 20,124,936 Total investments in fixed maturity securities $ 20,915,245 $ (36,751) $ 114,228 $ (811,175) $ 20,181,547 $ 20,178,308
Debt Securities, Held-to-maturity, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 43 $ 114 Provision for expected credit losses (5) (7) Allowance for expected credit losses, end of period $ 38 $ 107
Debt Securities, Available-for-sale, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2024 and 2023: 2024 2023 (In thousands) Foreign Government Corporate Mortgage-backed Asset-backed State and Municipal Total Foreign Government Corporate Mortgage-backed Total Allowance for expected credit losses, beginning of period $ 29,603 $ 5,026 $ 158 $ 1,164 $ 757 $ 36,708 $ 32,633 $ 4,701 $ 18 $ 37,352 Expected credit losses on securities for which credit losses were not previously recorded — — 562 — — 562 — 186 — 186 Expected credit (gains) losses on securities for which credit losses were previously recorded (9,124) (5,026) (158) (67) (64) (14,439) 691 (1,087) 5 (391) Reduction due to disposals — — — — — — — (5) — (5) Allowance for expected credit losses, end of period $ 20,479 $ — $ 562 $ 1,097 $ 693 $ 22,831 $ 33,324 $ 3,795 $ 23 $ 37,142
Amortized cost and fair value of fixed maturity securities by contractual maturity	The amortized cost and fair value of fixed maturity securities at March 31, 2024, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations. (In thousands) Amortized Fair Due in one year or less $ 1,980,563 $ 1,907,003 Due after one year through five years 9,877,133 9,528,047 Due after five years through ten years 4,681,226 4,577,859 Due after ten years 2,640,386 2,543,441 Mortgage-backed securities 2,596,170 2,410,862 Total $ 21,775,478 $ 20,967,212 ________________

Investments in Equity Securit_2

Investments in Equity Securities (Tables)	3 Months Ended
Investments in Equity Securities (Tables)	Mar. 31, 2024
Equity securities
Debt Securities, Available-for-sale [Line Items]
Schedule of Investments in Equity Securities	At March 31, 2024 and December 31, 2023, investments in equity securities were as follows: (In thousands) Cost Gross Unrealized Fair Carrying Gains Losses March 31, 2024 Common stocks $ 671,958 $ 196,093 $ (21,382) $ 846,669 $ 846,669 Preferred stocks 339,263 8,491 (16,375) 331,379 331,379 Total $ 1,011,221 $ 204,584 $ (37,757) $ 1,178,048 $ 1,178,048 December 31, 2023 Common stocks $ 664,997 $ 191,806 $ (18,749) $ 838,054 $ 838,054 Preferred stocks 284,335 3,075 (35,117) 252,293 252,293 Total $ 949,332 $ 194,881 $ (53,866) $ 1,090,347 $ 1,090,347

Net Investment Income (Tables)

Net Investment Income (Tables)	3 Months Ended
Net Investment Income (Tables)	Mar. 31, 2024
Net Investment Income [Abstract]
Schedule of Net Investment Income	Net investment income consisted of the following: For the Three Months (In thousands) 2024 2023 Investment income (loss) earned on: Fixed maturity securities, including cash and cash equivalents and loans receivable $ 335,248 $ 195,642 Arbitrage trading account (1) 18,011 18,256 Equity securities 11,336 13,746 Investment funds (29,349) 2,180 Real estate (13,163) (3,711) Gross investment income 322,083 226,113 Investment expense (2,244) (2,715) Net investment income $ 319,839 $ 223,398

Investment Funds (Tables)

Investment Funds (Tables)	3 Months Ended
Investment Funds (Tables)	Mar. 31, 2024
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Investment Funds	Investment funds consisted of the following: Carrying Value as of Income (Loss) from March 31, December 31, For the Three Months (In thousands) 2024 2023 2024 2023 Financial services $ 418,877 $ 433,407 $ (13,491) $ (13,047) Transportation 296,021 344,278 (28,661) 11,788 Real Estate 189,309 201,625 5,356 956 Infrastructure 137,201 130,589 5,039 3,355 Energy 134,195 114,794 8,632 3,439 Other funds 380,215 396,962 (6,224) (4,311) Total $ 1,555,818 $ 1,621,655 $ (29,349) $ 2,180

Real Estate (Tables)

Real Estate (Tables)	3 Months Ended
Real Estate (Tables)	Mar. 31, 2024
Real Estate [Abstract]
Schedule of Real Estate Investments	Investment in real estate represents directly owned property held for investment, as follows: Carrying Value March 31, December 31, (In thousands) 2024 2023 Properties in operation $ 1,045,712 $ 1,022,654 Properties under development 227,351 227,220 Total $ 1,273,063 $ 1,249,874

Loans Receivable Loans Receivab

Loans Receivable Loans Receivable (Tables)	3 Months Ended
Loans Receivable Loans Receivable (Tables)	Mar. 31, 2024
Receivables [Abstract]
Schedule of Loans Receivable	At March 31, 2024 and December 31, 2023, loans receivable were as follows: (In thousands) March 31, December 31, Amortized cost (net of allowance for expected credit losses): Real estate loans $ 227,431 $ 200,381 Commercial loans 1,335 890 Total $ 228,766 $ 201,271 Fair value: Real estate loans $ 227,821 $ 197,354 Commercial loans 1,335 890 Total $ 229,156 $ 198,244
Financing Receivable, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2024 and 2023: 2024 2023 (In thousands) Real Estate Loans Commercial Loans Total Real Estate Loans Commercial Loans Total Allowance for expected credit losses, beginning of period $ 2,983 $ 21 $ 3,004 $ 1,100 $ 691 $ 1,791 Change in expected credit losses (396) 1 (395) (61) (121) (182) Allowance for expected credit losses, end of period $ 2,587 $ 22 $ 2,609 $ 1,039 $ 570 $ 1,609

Net Investment (Losses) Gains (

Net Investment (Losses) Gains (Tables)	3 Months Ended
Net Investment (Losses) Gains (Tables)	Mar. 31, 2024
Realized and Unrealized Investment Gains (Losses) [Abstract]
Realized And Unrealized Investment Gains (Losses)	Net investment gains were as follows: For the Three Months (In thousands) 2024 2023 Net investment gains: Fixed maturity securities: Gains $ 3,557 $ 943 Losses (2,323) (18,130) Equity securities (1): Net realized gains on investment sales 40,277 1,060 Change in unrealized gains 25,812 43,404 Investment funds 993 10 Real estate (2,216) 10,739 Loans receivable — — Other (2) (54,597) (15,415) Net realized and unrealized gains on investments in earnings before allowance for expected credit losses 11,503 22,611 Change in allowance for expected credit losses on investments: Fixed maturity securities 13,882 217 Loans receivable 395 182 Change in allowance for expected credit losses on investments 14,277 399 Net investment gains 25,780 23,010 Income tax expense (6,633) (4,850) After-tax net investment gains $ 19,147 $ 18,160 Change in unrealized investment (losses) gains on available for sale securities: Fixed maturity securities without allowance for expected credit losses $ (88,594) $ 227,116 Fixed maturity securities with allowance for expected credit losses 987 3,456 Investment funds (1,703) 1,936 Other 13 (487) Total change in unrealized investment (losses) gains (89,297) 232,021 Income tax benefit (expense) 19,175 (51,222) Noncontrolling interests — (1) After-tax change in unrealized investment (losses) gains of available for sale securities $ (70,122) $ 180,798 ______________________ (1) The net realized gains or losses on investment sales represent the total gains or losses from the purchase dates of the equity securities. The change in unrealized gains (losses) consists of two components: (i) the reversal of the gain or loss recognized in previous periods on equity securities sold and (ii) the change in unrealized gain or loss resulting from mark-to-market adjustments on equity securities still held.

Fixed Maturity Securities In _2

Fixed Maturity Securities In An Unrealized Loss Position (Tables)	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Securities in an unrealized loss position	The following tables summarize all fixed maturity securities in an unrealized loss position at March 31, 2024 and December 31, 2023 by the length of time those securities have been continuously in an unrealized loss position: Less Than 12 Months 12 Months or Greater Total (In thousands) Fair Gross Fair Gross Fair Gross March 31, 2024 U.S. government and government agency $ 439,699 $ 6,725 $ 666,947 $ 48,531 $ 1,106,646 $ 55,256 State and municipal 308,609 3,376 1,764,296 120,513 2,072,905 123,889 Mortgage-backed 288,696 5,023 1,374,227 189,936 1,662,923 194,959 Asset-backed 1,055,695 3,765 1,282,145 60,820 2,337,840 64,585 Corporate 1,532,300 16,754 4,372,753 231,251 5,905,053 248,005 Foreign government 321,236 5,078 754,322 169,269 1,075,558 174,347 Fixed maturity securities $ 3,946,235 $ 40,721 $ 10,214,690 $ 820,320 $ 14,160,925 $ 861,041 December 31, 2023 U.S. government and government agency $ 384,392 $ 6,655 $ 614,623 $ 51,014 $ 999,015 $ 57,669 State and municipal 264,273 3,013 1,680,034 119,449 1,944,307 122,462 Mortgage-backed 278,819 2,025 1,360,748 175,131 1,639,567 177,156 Asset-backed 413,511 2,070 2,176,035 71,136 2,589,546 73,206 Corporate 874,754 11,975 4,418,309 231,288 5,293,063 243,263 Foreign government 204,908 1,758 794,174 135,661 999,082 137,419 Fixed maturity securities $ 2,420,657 $ 27,496 $ 11,043,923 $ 783,679 $ 13,464,580 $ 811,175
Non-Investment Grade Fixed Maturity Securities	A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2024 is presented in the table below: ($ in thousands) Number of Aggregate Gross Foreign government 36 $ 93,212 $ 141,742 State and municipal 5 24,438 4,918 Corporate 25 42,772 2,291 Mortgage-backed 15 4,526 237 Asset-backed 4 86 70 Total 85 $ 165,034 $ 149,258

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
Fair Value Measurements (Tables)	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Assets And Liabilities Measured At Fair value, On A Recurring Basis	The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023 by level: (In thousands) Total Level 1 Level 2 Level 3 March 31, 2024 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 1,829,552 $ — $ 1,829,552 $ — State and municipal 2,552,786 — 2,552,786 — Mortgage-backed 2,408,018 — 2,408,018 — Asset-backed 4,239,561 — 4,239,561 — Corporate 8,162,703 — 8,162,703 — Foreign government 1,718,252 — 1,718,252 — Total fixed maturity securities available for sale 20,910,872 — 20,910,872 — Equity securities: Common stocks 846,669 843,441 1,059 2,169 Preferred stocks 331,379 — 327,743 3,636 Total equity securities 1,178,048 843,441 328,802 5,805 Arbitrage trading account 1,146,119 752,159 390,284 3,676 Total $ 23,235,039 $ 1,595,600 $ 21,629,958 $ 9,481 Liabilities: Trading account securities sold but not yet purchased $ 40,298 $ 40,298 $ — $ — December 31, 2023 Assets: Fixed maturity securities available for sale: U.S. government and government agency $ 1,716,731 $ — $ 1,716,731 $ — State and municipal 2,634,422 — 2,634,422 — Mortgage-backed 2,266,455 — 2,266,455 — Asset-backed 4,187,040 — 4,187,040 — Corporate 7,654,059 — 7,654,059 — Foreign government 1,666,229 — 1,666,229 — Total fixed maturity securities available for sale 20,124,936 — 20,124,936 — Equity securities: Common stocks 838,054 835,338 1,158 1,558 Preferred stocks 252,293 — 248,598 3,695 Total equity securities 1,090,347 835,338 249,756 5,253 Arbitrage trading account 938,049 546,110 388,167 3,772 Total $ 22,153,332 $ 1,381,448 $ 20,762,859 $ 9,025 Liabilities: Trading account securities sold but not yet purchased $ 9,357 $ 9,357 $ — $ —
Summarize Changes In Level 3 Assets	The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2024 and for the year ended December 31, 2023: Gains (Losses) Included In: (In thousands) Beginning Earnings (Losses) Other Impairments Purchases Sales Paydowns / Maturities Transfers In / (Out) Ending Three Months Ended March 31, 2024 Assets: Equity securities: Common stocks $ 1,558 $ 611 $ — $ — $ — $ — $ — $ — $ 2,169 Preferred stocks 3,695 (2) — — — (57) — — 3,636 Total 5,253 609 — — — (57) — — 5,805 Arbitrage trading account 3,772 (133) — — — — — 37 3,676 Total $ 9,025 $ 476 $ — $ — $ — $ (57) $ — $ 37 $ 9,481 Year Ended Assets: Equity securities: Common stocks $ 2,599 $ (1,041) $ — $ — $ — $ — $ — $ — $ 1,558 Preferred stocks 11,299 (3) — (7,601) — — — — 3,695 Total 13,898 (1,044) — (7,601) — — — — 5,253 Arbitrage trading account 3,590 117 — — — — — 65 3,772 Total $ 17,488 $ (927) $ — $ (7,601) $ — $ — $ — $ 65 $ 9,025

Reserves for Loss and Loss Ex_2

Reserves for Loss and Loss Expenses (Tables)	3 Months Ended
Reserves for Loss and Loss Expenses (Tables)	Mar. 31, 2024
Insurance [Abstract]
Reserve Balances	The table below provides a reconciliation of the beginning and ending reserve balances: March 31, (In thousands) 2024 2023 Net reserves at beginning of period $ 15,661,820 $ 14,248,879 Net provision for losses and loss expenses: Claims occurring during the current year (1) 1,647,674 1,502,817 Increase in estimates for claims occurring in prior years (2) (3) 7,367 28,205 Loss reserve discount accretion 8,737 7,733 Total 1,663,778 1,538,755 Net payments for claims: Current year 107,434 110,274 Prior years 1,158,864 1,106,481 Total 1,266,298 1,216,755 Foreign currency translation (52,944) 1,154 Net reserves at end of period 16,006,356 14,572,033 Ceded reserves at end of period 3,093,272 2,859,602 Gross reserves at end of period $ 19,099,628 $ 17,431,635 _______________________________________ (1) Claims occurring during the current year are net of loss reserve discounts of $14 million and $11 million for the three months ended March 31, 2024 and 2023, respectively. (2) The change in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years decreased by $10 million and increased by $19 million for the three months ended March 31, 2024 and 2023, respectively. (3) For certain retrospectively rated insurance policies and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable development, net of additional and return premiums, was $1 million and adverse development was $24 million for the three months ended March 31, 2024 and 2023, respectively.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
Fair Value of Financial Instruments (Tables)	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Carrying Amounts And Estimated Fair Values Of Financial Instruments	The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments: March 31, 2024 December 31, 2023 (In thousands) Carrying Value Fair Value Carrying Value Fair Value Assets: Fixed maturity securities $ 20,964,854 $ 20,967,212 $ 20,178,308 $ 20,181,547 Equity securities 1,178,048 1,178,048 1,090,347 1,090,347 Arbitrage trading account 1,146,119 1,146,119 938,049 938,049 Loans receivable 228,766 229,156 201,271 198,244 Cash and cash equivalents 1,169,053 1,169,053 1,363,195 1,363,195 Trading account receivables from brokers and clearing organizations 141,277 141,277 303,614 303,614 Due from broker — — 36,747 36,747 Liabilities: Due to broker 33,027 33,027 — — Trading account securities sold but not yet purchased 40,298 40,298 9,357 9,357 Senior notes and other debt 1,827,997 1,435,877 1,827,951 1,480,076 Subordinated debentures 1,009,269 893,358 1,009,090 929,598

Premiums and Reinsurance Rela_2

Premiums and Reinsurance Related Information (Tables)	3 Months Ended
Premiums and Reinsurance Related Information (Tables)	Mar. 31, 2024
Insurance [Abstract]
Reinsurance Financial Information	The following is a summary of insurance and reinsurance financial information: For the Three Months (In thousands) 2024 2023 Written premiums: Direct $ 3,039,066 $ 2,738,754 Assumed 323,689 310,563 Ceded (511,464) (474,493) Total net premiums written $ 2,851,291 $ 2,574,824 Earned premiums: Direct $ 2,936,643 $ 2,667,063 Assumed 337,911 295,230 Ceded (510,207) (470,861) Total net premiums earned $ 2,764,347 $ 2,491,432 Ceded losses and loss expenses incurred $ 305,951 $ 315,476 Ceded commissions earned $ 121,054 $ 118,418
Premium receivable, allowance for credit loss	The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 35,110 $ 30,660 Change in expected credit losses (71) 1,693 Allowance for expected credit losses, end of period $ 35,039 $ 32,353
Reinsurance Recoverable, Allowance for Credit Loss	The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2024 and 2023: (In thousands) 2024 2023 Allowance for expected credit losses, beginning of period $ 8,404 $ 8,064 Change in expected credit losses 781 639 Allowance for expected credit losses, end of period $ 9,185 $ 8,703

Restricted Stock Units (Tables)

Restricted Stock Units (Tables)	3 Months Ended
Restricted Stock Units (Tables)	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Summary Of Restricted Stock Units Issued	A summary of RSUs issued in the three months ended March 31, 2024 and 2023 follows: ($ in thousands) Units Fair Value 2024 1,214 $ 100 2023 — $ —

Leases (Tables)

Leases (Tables)	3 Months Ended
Leases (Tables)	Mar. 31, 2024
Leases [Abstract]
Lease, Cost	Further information relating to operating lease expense and other operating lease information are as follows: For the Three Months Ended (In thousands) 2024 2023 Leases: Lease cost $ 11,077 $ 10,188 Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows $ 12,232 $ 10,563 Right-of-use assets obtained in exchange for new lease liabilities $ 24,695 $ 5,313
Supplemental Balance Sheet Information	As of March 31, ($ in thousands) 2024 2023 Right-of-use assets $ 191,720 $ 164,547 Lease liabilities $ 233,114 $ 199,225 Weighted-average remaining lease term 7.6 years 7.1 years Weighted-average discount rate 5.44 % 4.49 %
Maturities of Operating Lease Liabilities	Contractual maturities of the Company’s future minimum lease payments are as follows: (In thousands) March 31, 2024 Contractual Maturities: 2024 $ 38,862 2025 44,402 2026 37,499 2027 28,341 2028 26,760 Thereafter 104,223 Total undiscounted future minimum lease payments 280,087 Less: Discount impact 46,973 Total lease liability $ 233,114

Business Segments (Tables)

Business Segments (Tables)	3 Months Ended
Business Segments (Tables)	Mar. 31, 2024
Segment Reporting [Abstract]
Financial Information Of Company Operating Segments	Revenues (In thousands) Earned Investment Other Total (2) Pre-Tax Income (Loss) Net Income (Loss) to Common Stockholders Three months ended March 31, 2024 Insurance $ 2,398,768 $ 244,778 $ 9,423 $ 2,652,969 $ 478,149 $ 365,091 Reinsurance & Monoline Excess 365,579 53,211 — 418,790 127,624 102,126 Corporate, other and eliminations (3) — 21,850 137,384 159,234 (57,482) (43,893) Net investment gains — — 25,780 25,780 25,780 19,147 Total $ 2,764,347 $ 319,839 $ 172,587 $ 3,256,773 $ 574,071 $ 442,471 Three months ended March 31, 2023 Insurance $ 2,142,924 $ 163,558 $ 9,577 $ 2,316,059 $ 352,626 $ 274,108 Reinsurance & Monoline Excess 348,508 54,583 — 403,091 101,285 82,357 Corporate, other and eliminations (3) — 5,257 147,587 152,844 (100,850) (80,499) Net investment gains — — 23,010 23,010 23,010 18,160 Total $ 2,491,432 $ 223,398 $ 180,174 $ 2,895,004 $ 376,071 $ 294,126 _________________ (1) Certain amounts included in earned premiums of each segment are related to inter-segment transactions. (2) Revenues for Insurance from foreign operations for the three months ended March 31, 2024 and 2023 were $393 million and $274 million, respectively. Revenues for Reinsurance & Monoline Excess from foreign operations for the three months ended March 31, 2024 and 2023 were $111 million and $106 million, respectively.
Identifiable Assets By Segment	(In thousands) March 31, December 31, Insurance $ 30,048,006 $ 29,923,282 Reinsurance & Monoline Excess 5,506,533 5,545,249 Corporate, other and eliminations 2,296,533 1,643,299 Consolidated $ 37,851,072 $ 37,111,830
Net Premiums Earned By Major Line Of Business	Net premiums earned by major line of business are as follows: For the Three Months (In thousands) 2024 2023 Insurance: Other liability $ 967,260 $ 853,472 Short-tail lines (1) 510,809 412,534 Auto 354,013 294,116 Workers' compensation 301,495 305,561 Professional liability 265,191 277,241 Total Insurance 2,398,768 2,142,924 Reinsurance & Monoline Excess: Casualty (2) 197,844 214,712 Property (2) 102,384 75,152 Monoline excess (3) 65,351 58,644 Total Reinsurance & Monoline Excess 365,579 348,508 Total $ 2,764,347 $ 2,491,432 ______________ (1) Short-tail lines include commercial multi-peril (non-liability), inland marine, accident and health, fidelity and surety, boiler and machinery, high net worth homeowners and other lines. (2) Includes reinsurance casualty and property and certain program management business.

Consolidated Statements of Co_4

Consolidated Statements of Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	$ 7,469,237
Other comprehensive (loss) income	(97,692)	$ 185,665
End of period	7,798,512
Net realized and unrealized gains on investments	11,503	22,611
Income before income taxes	574,071	376,071
Tax effect	(132,036)	(80,342)
Net income before noncontrolling interests	442,035	295,729
Total change in unrealized investment (losses) gains	(89,297)	232,021
Net change in period	(27,570)	4,866
Other comprehensive income (loss), pre-tax	(116,867)	236,887
Other comprehensive income (loss), tax effect	19,175	(51,222)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(925,838)	(1,264,581)
Other comprehensive loss before reclassifications	(128,882)	160,081
Amounts reclassified from AOCI	31,190	25,584
Other comprehensive (loss) income	(97,692)	185,665
Unrealized investment loss related to noncontrolling interest	0	(1)
End of period	(1,023,530)	(1,078,917)
Accumulated Other Comprehensive Income (Loss) \| Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income before income taxes	39,481	32,385
Tax effect	(8,291)	(6,801)
Net income before noncontrolling interests	31,190	25,584
Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(586,354)	(892,905)
Other comprehensive loss before reclassifications	(101,312)	155,215
Amounts reclassified from AOCI	31,190	25,584
Other comprehensive (loss) income	(70,122)	180,799
Unrealized investment loss related to noncontrolling interest	0	(1)
End of period	(656,476)	(712,107)
Total change in unrealized investment (losses) gains	(89,297)	232,021
Unrealized investment gains, tax effect	19,175	(51,222)
Unrealized investment gains (losses), after-tax amounts	(70,122)	180,799
Unrealized Investment Gains (Losses) \| Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net realized and unrealized gains on investments	39,481	32,385
Tax effect	(8,291)	(6,801)
Net income before noncontrolling interests	31,190	25,584
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of period	(339,484)	(371,676)
Other comprehensive loss before reclassifications	(27,570)	4,866
Amounts reclassified from AOCI	0	0
Other comprehensive (loss) income	(27,570)	4,866
Unrealized investment loss related to noncontrolling interest	0	0
End of period	(367,054)	(366,810)
Currency translation adjustment, pre-tax	(27,570)	4,866
Currency translation adjustment, tax effect	0	0
Net change in period	(27,570)	4,866
Currency Translation Adjustments \| Amounts reclassified from AOCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Income before income taxes	0	0
Tax effect	0	0
Net income before noncontrolling interests	$ 0	$ 0

Statements of Cash Flows (Detai

Statements of Cash Flows (Details) - USD ($)	3 Months Ended
Statements of Cash Flows (Details) - USD ($)	Mar. 31, 2024	Mar. 31, 2023
Supplemental Cash Flow Elements [Abstract]
Interest payments	$ 28,577,000	$ 41,150,000
Income taxes paid	$ 0	$ 0

Per Share Data (Narrative) (Det

Per Share Data (Narrative) (Details) - shares	3 Months Ended
Per Share Data (Narrative) (Details) - shares	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Weighted average number of shares held in grantor trust (in shares)	11,663,450,000	11,416,856

Per Share Data (Weighted Averag

Per Share Data (Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share) (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Basic (shares)	268,211	274,977
Diluted (shares)	270,505	277,339

Investments in Fixed Maturity_3

Investments in Fixed Maturity Securities (Investments in fixed maturity securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Total held to maturity, Amortized Cost	$ 54,020	$ 53,415
Held-to-maturity, Allowance for Credit Loss	(38)	(43)	$ (107)	$ (114)
Held to maturity, Gross Unrealized Gains	2,358	3,239
Held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	56,340	56,611
Total held to maturity, Carrying Value	53,982	53,372
Total available for sale, Amortized Cost	21,721,496	20,861,830
Available-for-sale, Allowance for Credit Loss	(22,831)	(36,708)	(37,142)	(37,352)
Total available for sale, Gross Unrealized Gains	73,248	110,989
Total available for sale, Gross Unrealized Losses	(861,041)	(811,175)
Total available for sale, Fair Value	20,910,872	20,124,936
Total fixed maturity securities available for sale	20,910,872	20,124,936
Total investments in fixed maturity securities, Amortized Value	21,775,516	20,915,245
Fixed maturity securities, allowance for credit loss	(22,869)	(36,751)
Total investments in fixed maturity securities, Gross Unrealized Gains	75,606	114,228
Total investments in fixed maturity securities, Gross Unrealized Losses	(861,041)	(811,175)
Total investments in fixed maturity securities, Fair Value	20,967,212	20,181,547
Total investments in fixed maturity securities, Carrying Value	20,964,854	20,178,308
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total held to maturity, Amortized Cost	51,258	50,547
Held-to-maturity, Allowance for Credit Loss	(38)	(43)
Held to maturity, Gross Unrealized Gains	2,276	3,132
Held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	53,496	53,636
Total held to maturity, Carrying Value	51,220	50,504
Total available for sale, Amortized Cost	2,668,420	2,742,922
Available-for-sale, Allowance for Credit Loss	(693)	(757)
Total available for sale, Gross Unrealized Gains	8,948	14,719
Total available for sale, Gross Unrealized Losses	(123,889)	(122,462)
Total available for sale, Fair Value	2,552,786	2,634,422
Total fixed maturity securities available for sale	2,552,786	2,634,422
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total held to maturity, Amortized Cost	2,762	2,868
Held-to-maturity, Allowance for Credit Loss	0	0
Held to maturity, Gross Unrealized Gains	82	107
Held to maturity, Gross Unrealized Losses	0	0
Total held to maturity, Fair Value	2,844	2,975
Total held to maturity, Carrying Value	2,762	2,868
Total available for sale, Amortized Cost	1,963,060	1,773,206
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	9,805	12,780
Total available for sale, Gross Unrealized Losses	(174,727)	(163,844)
Total available for sale, Fair Value	1,798,138	1,622,142
Total fixed maturity securities available for sale	1,798,138	1,622,142
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	1,875,920	1,762,997
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	8,888	11,403
Total available for sale, Gross Unrealized Losses	(55,256)	(57,669)
Total available for sale, Fair Value	1,829,552	1,716,731
Total fixed maturity securities available for sale	1,829,552	1,716,731
Special revenue
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	1,626,511	1,682,550
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	3,370	5,651
Total available for sale, Gross Unrealized Losses	(83,769)	(82,006)
Total available for sale, Fair Value	1,546,112	1,606,195
Total fixed maturity securities available for sale	1,546,112	1,606,195
State general obligation
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	393,807	394,429
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	1,833	3,550
Total available for sale, Gross Unrealized Losses	(16,316)	(16,405)
Total available for sale, Fair Value	379,324	381,574
Total fixed maturity securities available for sale	379,324	381,574
Pre-refunded
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	88,359	103,029
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	908	1,634
Total available for sale, Gross Unrealized Losses	(214)	(185)
Total available for sale, Fair Value	89,053	104,478
Total fixed maturity securities available for sale	89,053	104,478
Corporate backed
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	166,261	166,873
Available-for-sale, Allowance for Credit Loss	(693)	(757)
Total available for sale, Gross Unrealized Gains	539	696
Total available for sale, Gross Unrealized Losses	(10,588)	(11,973)
Total available for sale, Fair Value	155,519	154,839
Total fixed maturity securities available for sale	155,519	154,839
Local general obligation
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	393,482	396,041
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	2,298	3,188
Total available for sale, Gross Unrealized Losses	(13,002)	(11,893)
Total available for sale, Fair Value	382,778	387,336
Total fixed maturity securities available for sale	382,778	387,336
Commercial
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	630,348	657,157
Available-for-sale, Allowance for Credit Loss	(562)	(158)
Total available for sale, Gross Unrealized Gains	326	626
Total available for sale, Gross Unrealized Losses	(20,232)	(13,312)
Total available for sale, Fair Value	609,880	644,313
Total fixed maturity securities available for sale	609,880	644,313
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	2,593,408	2,430,363
Available-for-sale, Allowance for Credit Loss	(562)	(158)	(23)	(18)
Total available for sale, Gross Unrealized Gains	10,131	13,406
Total available for sale, Gross Unrealized Losses	(194,959)	(177,156)
Total available for sale, Fair Value	2,408,018	2,266,455
Total fixed maturity securities available for sale	2,408,018	2,266,455
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	4,298,768	4,252,883
Available-for-sale, Allowance for Credit Loss	(1,097)	(1,164)
Total available for sale, Gross Unrealized Gains	6,475	8,527
Total available for sale, Gross Unrealized Losses	(64,585)	(73,206)
Total available for sale, Fair Value	4,239,561	4,187,040
Total fixed maturity securities available for sale	4,239,561	4,187,040
Industrial
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	3,865,664	3,679,219
Available-for-sale, Allowance for Credit Loss	0	(40)
Total available for sale, Gross Unrealized Gains	14,741	24,312
Total available for sale, Gross Unrealized Losses	(146,130)	(143,936)
Total available for sale, Fair Value	3,734,275	3,559,555
Total fixed maturity securities available for sale	3,734,275	3,559,555
Financial
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	3,172,945	2,838,220
Available-for-sale, Allowance for Credit Loss	0	(4,986)
Total available for sale, Gross Unrealized Gains	10,100	14,681
Total available for sale, Gross Unrealized Losses	(69,749)	(68,681)
Total available for sale, Fair Value	3,113,296	2,779,234
Total fixed maturity securities available for sale	3,113,296	2,779,234
Utilities
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	751,234	701,865
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	2,864	6,471
Total available for sale, Gross Unrealized Losses	(24,436)	(23,412)
Total available for sale, Fair Value	729,662	684,924
Total fixed maturity securities available for sale	729,662	684,924
Other
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	590,644	635,975
Available-for-sale, Allowance for Credit Loss	0	0
Total available for sale, Gross Unrealized Gains	2,516	1,605
Total available for sale, Gross Unrealized Losses	(7,690)	(7,234)
Total available for sale, Fair Value	585,470	630,346
Total fixed maturity securities available for sale	585,470	630,346
Corporate
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	8,380,487	7,855,279
Available-for-sale, Allowance for Credit Loss	0	(5,026)	(3,795)	(4,701)
Total available for sale, Gross Unrealized Gains	30,221	47,069
Total available for sale, Gross Unrealized Losses	(248,005)	(243,263)
Total available for sale, Fair Value	8,162,703	7,654,059
Total fixed maturity securities available for sale	8,162,703	7,654,059
Foreign government
Debt Securities, Available-for-sale [Line Items]
Total available for sale, Amortized Cost	1,904,493	1,817,386
Available-for-sale, Allowance for Credit Loss	(20,479)	(29,603)	$ (33,324)	$ (32,633)
Total available for sale, Gross Unrealized Gains	8,585	15,865
Total available for sale, Gross Unrealized Losses	(174,347)	(137,419)
Total available for sale, Fair Value	1,718,252	1,666,229
Total fixed maturity securities available for sale	$ 1,718,252	$ 1,666,229

Investments in Fixed Maturity_4

Investments in Fixed Maturity Securities (HTM Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 43	$ 114
Cumulative effect adjustment resulting from changes in accounting principles	38	107
Provision for expected credit losses	(5)	(7)
Allowance for expected credit losses, end of period	$ 38	$ 107

Investments in Fixed Maturity_5

Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 36,708	$ 37,352
Expected credit losses on securities for which credit losses were not previously recorded	562	186
Expected credit (gains) losses on securities for which credit losses were previously recorded	(14,439)	(391)
Reduction due to disposals	0	(5)
Allowance for expected credit losses, end of period	22,831	37,142
Foreign government
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	29,603	32,633
Expected credit losses on securities for which credit losses were not previously recorded	0	0
Expected credit (gains) losses on securities for which credit losses were previously recorded	(9,124)	691
Reduction due to disposals	0	0
Allowance for expected credit losses, end of period	20,479	33,324
Corporate
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	5,026	4,701
Expected credit losses on securities for which credit losses were not previously recorded	0	186
Expected credit (gains) losses on securities for which credit losses were previously recorded	(5,026)	(1,087)
Reduction due to disposals	0	(5)
Allowance for expected credit losses, end of period	0	3,795
Mortgage-backed
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	158	18
Expected credit losses on securities for which credit losses were not previously recorded	562	0
Expected credit (gains) losses on securities for which credit losses were previously recorded	(158)	5
Reduction due to disposals	0	0
Allowance for expected credit losses, end of period	562	$ 23
Asset-backed
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	1,164
Expected credit losses on securities for which credit losses were not previously recorded	0
Expected credit (gains) losses on securities for which credit losses were previously recorded	(67)
Reduction due to disposals	0
Allowance for expected credit losses, end of period	1,097
State and municipal
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	757
Expected credit losses on securities for which credit losses were not previously recorded	0
Expected credit (gains) losses on securities for which credit losses were previously recorded	(64)
Reduction due to disposals	0
Allowance for expected credit losses, end of period	$ 693

Investments in Fixed Maturity_6

Investments in Fixed Maturity Securities (Amortized cost and fair value of fixed maturity securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 1,980,563
Amortized Cost, Due after one year through five years	9,877,133
Amortized Cost, Due after five years through ten years	4,681,226
Amortized Cost, Due after ten years	2,640,386
Amortized Cost, Mortgaged-backed securities	2,596,170
Total investments in fixed maturity securities, Amortized Value	21,775,478
Fair Value, Due in one year or less	1,907,003
Fair Value, Due after one year through five years	9,528,047
Fair Value, Due after five years through ten years	4,577,859
Fair Value, Due after ten years	2,543,441
Fair Value, Mortgage-backed securities	2,410,862
Total investments in fixed maturity securities, Fair Value	20,967,212	$ 20,181,547
Cumulative effect adjustment resulting from changes in accounting principles	$ 38	$ 43	$ 107	$ 114

Investments in Equity Securit_3

Investments in Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 1,178,048	$ 1,090,347
Fair Value
Debt Securities, Available-for-sale [Line Items]
Cost	1,011,221	949,332
Gross Unrealized, Gains	204,584	194,881
Gross Unrealized, Losses	(37,757)	(53,866)
Equity securities	1,178,048	1,090,347
Fair Value \| Common stock
Debt Securities, Available-for-sale [Line Items]
Cost	671,958	664,997
Gross Unrealized, Gains	196,093	191,806
Gross Unrealized, Losses	(21,382)	(18,749)
Equity securities	846,669	838,054
Fair Value \| Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Cost	339,263	284,335
Gross Unrealized, Gains	8,491	3,075
Gross Unrealized, Losses	(16,375)	(35,117)
Equity securities	331,379	252,293
Carrying Value
Debt Securities, Available-for-sale [Line Items]
Equity securities	1,178,048	1,090,347
Carrying Value \| Common stock
Debt Securities, Available-for-sale [Line Items]
Equity securities	846,669	838,054
Carrying Value \| Preferred stocks
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 331,379	$ 252,293

Arbitrage Trading Account (Deta

Arbitrage Trading Account (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Derivative [Line Items]
Arbitrage trading account	$ 1,146,000,000	$ 938,000,000
Long \| Options held
Derivative [Line Items]
Fair value of derivative	117,000
Notional amount of derivative	162,000,000
Short \| Options held
Derivative [Line Items]
Fair value of derivative	40,000,000
Notional amount of derivative	$ 162,000,000

Net Investment Income (Details)

Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended
Net Investment Income (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Net Investment Income [Line Items]
Gross investment income	$ 322,083	$ 226,113
Investment expense	(2,244)	(2,715)
Net investment income	319,839	223,398
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Gross investment income	335,248	195,642
Arbitrage trading account (1)
Net Investment Income [Line Items]
Gross investment income	(29,349)	2,180
Equity securities
Net Investment Income [Line Items]
Gross investment income	11,336	13,746
Investment funds
Net Investment Income [Line Items]
Gross investment income	18,011	18,256
Real estate
Net Investment Income [Line Items]
Gross investment income	$ (13,163)	$ (3,711)

Investment Funds (Details)

Investment Funds (Details) - USD ($) $ in Thousands		3 Months Ended		18 Months Ended
Investment Funds (Details) - USD ($) $ in Thousands	Jul. 01, 2022	Mar. 31, 2024	Mar. 31, 2023	Jun. 30, 2022	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Unfunded commitments		$ 309,000
Investment funds		1,555,818			$ 1,621,655
Income (Loss) from Investment Funds		(29,349)	$ 2,180
Written premiums ceded		511,464	474,493
Fair Value
Schedule of Equity Method Investments [Line Items]
Trading account receivables from brokers and clearing organizations		141,277			303,614
Lifson Re
Schedule of Equity Method Investments [Line Items]
Percentage of reinsurance placements of share placed amounts	30%			22.50%
Written premiums ceded		94,000	107,000
Financial services
Schedule of Equity Method Investments [Line Items]
Investment funds		189,309			201,625
Income (Loss) from Investment Funds		5,356	956
Transportation
Schedule of Equity Method Investments [Line Items]
Investment funds		418,877			433,407
Income (Loss) from Investment Funds		(13,491)	(13,047)
Real Estate
Schedule of Equity Method Investments [Line Items]
Investment funds		296,021			344,278
Income (Loss) from Investment Funds		(28,661)	11,788
Energy
Schedule of Equity Method Investments [Line Items]
Investment funds		134,195			114,794
Income (Loss) from Investment Funds		8,632	3,439
Infrastructure
Schedule of Equity Method Investments [Line Items]
Investment funds		137,201			130,589
Income (Loss) from Investment Funds		5,039	3,355
Other funds
Schedule of Equity Method Investments [Line Items]
Investment funds		380,215			396,962
Income (Loss) from Investment Funds		(6,224)	$ (4,311)
Deferred compensation trust assets		$ 41,000			$ 36,000

Real Estate (Details)

Real Estate (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Real Estate [Abstract]
Properties in operation	$ 1,045,712	$ 1,022,654
Properties under development	227,351	227,220
Total	$ 1,273,063	$ 1,249,874

Real Estate (Narrative) (Detail

Real Estate (Narrative) (Details) - USD ($)	3 Months Ended
Real Estate (Narrative) (Details) - USD ($)	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Real Estate [Abstract]
Accumulated depreciation and amortization on properties	$ 34,131,000		$ 32,745,000
Real estate depreciation expense	1,941,000	$ 2,281,000
Lease future minimum payments 2021	25,874,266
Lease future minimum payments 2022	33,742,431
Lease future minimum payments 2023	31,539,135
Lease future minimum payments 2024	30,794,160
Lease future minimum payments 2025	31,352,156
Lease future minimum payments 2026	26,899,553
Lease future minimum payments there after	$ 413,976,622

Loans Receivable (Details)

Loans Receivable (Details) - USD ($) $ in Thousands	3 Months Ended
Loans Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	$ 228,766	$ 201,271
Loans receivable	229,156	198,244
Real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	227,431	200,381
Loans receivable	227,821	197,354
Commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable, gross	1,335	890
Loans receivable	$ 1,335	$ 890
Loans receivable maturity term	10 years

Loans Receivable - Allowance Fo

Loans Receivable - Allowance For Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses, beginning of period	$ 3,004	$ 1,791
Change in expected credit losses	(395)	(182)
Allowance for expected credit losses, end of period	2,609	1,609
Real estate loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses, beginning of period	2,983	1,100
Change in expected credit losses	(396)	(61)
Allowance for expected credit losses, end of period	2,587	1,039
Commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for expected credit losses, beginning of period	21	691
Change in expected credit losses	1	(121)
Allowance for expected credit losses, end of period	$ 22	$ 570

Net Investment (Losses) Gains_2

Net Investment (Losses) Gains (Net Investment Gains (Losses)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Fixed maturity securities, gains	$ 3,557	$ 943
Fixed maturity securities, losses	(2,323)	(18,130)
Net realized gains on investment sales	40,277	1,060
Change in unrealized gains	25,812	43,404
Investment funds	993	10
Real estate	(2,216)	10,739
Loans receivable	0	0
Other (2)	(54,597)	(15,415)
Net realized and unrealized gains on investments in earnings before allowance for expected credit losses	11,503	22,611
Fixed maturity securities	13,882	217
Loans receivable	395	182
Change in allowance for expected credit losses on investments	14,277	399
Net investment gains	25,780	23,010
Income tax expense	(6,633)	(4,850)
After-tax net investment gains	$ 19,147	$ 18,160

Net Investment (Losses) Gains_3

Net Investment (Losses) Gains (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment (losses) gains	$ (89,297)	$ 232,021
Income tax benefit (expense)	19,175	(51,222)
Noncontrolling interests	0	(1)
Total change in unrealized gains	(70,122)	180,798
Debt securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment (losses) gains	(88,594)	227,116
Fixed maturity securities with allowance for expected credit losses
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment (losses) gains	987	3,456
Investment funds
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment (losses) gains	(1,703)	1,936
Other
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment (losses) gains	$ 13	$ (487)

Fixed Maturity Securities In _3

Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt securities
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	$ 3,946,235	$ 2,420,657
Gross Unrealized Losses, Less than 12 Months	40,721	27,496
Fair Value, 12 Months or Greater	10,214,690	11,043,923
Gross Unrealized Losses, 12 Months or Greater	820,320	783,679
Fair Value, Total	14,160,925	13,464,580
Gross Unrealized Losses, Total	861,041	811,175
U.S. government and government agency
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	439,699	384,392
Gross Unrealized Losses, Less than 12 Months	6,725	6,655
Fair Value, 12 Months or Greater	666,947	614,623
Gross Unrealized Losses, 12 Months or Greater	48,531	51,014
Fair Value, Total	1,106,646	999,015
Gross Unrealized Losses, Total	55,256	57,669
State and municipal
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	308,609	264,273
Gross Unrealized Losses, Less than 12 Months	3,376	3,013
Fair Value, 12 Months or Greater	1,764,296	1,680,034
Gross Unrealized Losses, 12 Months or Greater	120,513	119,449
Fair Value, Total	2,072,905	1,944,307
Gross Unrealized Losses, Total	123,889	122,462
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	288,696	278,819
Gross Unrealized Losses, Less than 12 Months	5,023	2,025
Fair Value, 12 Months or Greater	1,374,227	1,360,748
Gross Unrealized Losses, 12 Months or Greater	189,936	175,131
Fair Value, Total	1,662,923	1,639,567
Gross Unrealized Losses, Total	194,959	177,156
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,055,695	413,511
Gross Unrealized Losses, Less than 12 Months	3,765	2,070
Fair Value, 12 Months or Greater	1,282,145	2,176,035
Gross Unrealized Losses, 12 Months or Greater	60,820	71,136
Fair Value, Total	2,337,840	2,589,546
Gross Unrealized Losses, Total	64,585	73,206
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	1,532,300	874,754
Gross Unrealized Losses, Less than 12 Months	16,754	11,975
Fair Value, 12 Months or Greater	4,372,753	4,418,309
Gross Unrealized Losses, 12 Months or Greater	231,251	231,288
Fair Value, Total	5,905,053	5,293,063
Gross Unrealized Losses, Total	248,005	243,263
Foreign government
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 Months	321,236	204,908
Gross Unrealized Losses, Less than 12 Months	5,078	1,758
Fair Value, 12 Months or Greater	754,322	794,174
Gross Unrealized Losses, 12 Months or Greater	169,269	135,661
Fair Value, Total	1,075,558	999,082
Gross Unrealized Losses, Total	$ 174,347	$ 137,419

Fixed Maturity Securities In _4

Fixed Maturity Securities In An Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) - External Credit Rating, Non Investment Grade $ in Thousands	Mar. 31, 2024 USD ($)
Foreign government
Debt Securities, Available-for-sale [Line Items]
Number of Securities	36
Aggregate Fair Value	$ 93,212
Gross Unrealized Loss	$ 141,742
State and municipal
Debt Securities, Available-for-sale [Line Items]
Number of Securities	5
Aggregate Fair Value	$ 24,438
Gross Unrealized Loss	$ 4,918
Corporate
Debt Securities, Available-for-sale [Line Items]
Number of Securities	25
Aggregate Fair Value	$ 42,772
Gross Unrealized Loss	$ 2,291
Mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Number of Securities	15
Aggregate Fair Value	$ 4,526
Gross Unrealized Loss	$ 237
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Number of Securities	4
Aggregate Fair Value	$ 86
Gross Unrealized Loss	$ 70
Special revenue
Debt Securities, Available-for-sale [Line Items]
Number of Securities	85
Aggregate Fair Value	$ 165,034
Gross Unrealized Loss	$ 149,258

Fair Value Measurements (Assets

Fair Value Measurements (Assets and Liabilities Measured At Fair Value, On a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Total fixed maturity securities available for sale	$ 20,910,872	$ 20,124,936
Equity securities	1,178,048	1,090,347
Arbitrage trading account	1,146,000	938,000
Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	20,910,872	20,124,936
Equity securities	1,178,048	1,090,347
Arbitrage trading account	1,146,119	938,049
Total	23,235,039	22,153,332
Liabilities:
Trading account securities sold but not yet purchased	40,298	9,357
Fair Value, Measurements, Recurring \| U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	1,829,552	1,716,731
Fair Value, Measurements, Recurring \| State and municipal
Assets:
Total fixed maturity securities available for sale	2,552,786	2,634,422
Fair Value, Measurements, Recurring \| Mortgage-backed
Assets:
Total fixed maturity securities available for sale	2,408,018	2,266,455
Fair Value, Measurements, Recurring \| Asset-backed
Assets:
Total fixed maturity securities available for sale	4,239,561	4,187,040
Fair Value, Measurements, Recurring \| Corporate
Assets:
Total fixed maturity securities available for sale	8,162,703	7,654,059
Fair Value, Measurements, Recurring \| Foreign government
Assets:
Total fixed maturity securities available for sale	1,718,252	1,666,229
Fair Value, Measurements, Recurring \| Common stocks
Assets:
Equity securities	846,669	838,054
Fair Value, Measurements, Recurring \| Preferred stocks
Assets:
Equity securities	331,379	252,293
Level 1 \| Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	0	0
Equity securities	843,441	835,338
Arbitrage trading account	752,159	546,110
Total	1,595,600	1,381,448
Liabilities:
Trading account securities sold but not yet purchased	40,298	9,357
Level 1 \| Fair Value, Measurements, Recurring \| U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| State and municipal
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Mortgage-backed
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Asset-backed
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Corporate
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Foreign government
Assets:
Total fixed maturity securities available for sale	0	0
Level 1 \| Fair Value, Measurements, Recurring \| Common stocks
Assets:
Equity securities	843,441	835,338
Level 1 \| Fair Value, Measurements, Recurring \| Preferred stocks
Assets:
Equity securities	0	0
Level 2 \| Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	20,910,872	20,124,936
Equity securities	328,802	249,756
Arbitrage trading account	390,284	388,167
Total	21,629,958	20,762,859
Liabilities:
Trading account securities sold but not yet purchased	0	0
Level 2 \| Fair Value, Measurements, Recurring \| U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	1,829,552	1,716,731
Level 2 \| Fair Value, Measurements, Recurring \| State and municipal
Assets:
Total fixed maturity securities available for sale	2,552,786	2,634,422
Level 2 \| Fair Value, Measurements, Recurring \| Mortgage-backed
Assets:
Total fixed maturity securities available for sale	2,408,018	2,266,455
Level 2 \| Fair Value, Measurements, Recurring \| Asset-backed
Assets:
Total fixed maturity securities available for sale	4,239,561	4,187,040
Level 2 \| Fair Value, Measurements, Recurring \| Corporate
Assets:
Total fixed maturity securities available for sale	8,162,703	7,654,059
Level 2 \| Fair Value, Measurements, Recurring \| Foreign government
Assets:
Total fixed maturity securities available for sale	1,718,252	1,666,229
Level 2 \| Fair Value, Measurements, Recurring \| Common stocks
Assets:
Equity securities	1,059	1,158
Level 2 \| Fair Value, Measurements, Recurring \| Preferred stocks
Assets:
Equity securities	327,743	248,598
Level 3 \| Fair Value, Measurements, Recurring
Assets:
Total fixed maturity securities available for sale	0	0
Equity securities	5,805	5,253
Arbitrage trading account	3,676	3,772
Total	9,481	9,025
Liabilities:
Trading account securities sold but not yet purchased	0	0
Level 3 \| Fair Value, Measurements, Recurring \| U.S. government and government agency
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| State and municipal
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Mortgage-backed
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Asset-backed
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Corporate
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Foreign government
Assets:
Total fixed maturity securities available for sale	0	0
Level 3 \| Fair Value, Measurements, Recurring \| Common stocks
Assets:
Equity securities	2,169	1,558
Level 3 \| Fair Value, Measurements, Recurring \| Preferred stocks
Assets:
Equity securities	$ 3,636	$ 3,695

Fair Value Measurements (Summar

Fair Value Measurements (Summarize Changes in Level 3 Assets) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, Impairments		$ (7,601)
Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	$ 9,025	17,488
Assets, earnings	476	(927)
Assets, other comprehensive income	0	0
Assets, Impairments	0
Assets, purchases	0	0
Assets, (sales)	(57)	0
Assets, maturities	0	0
Assets. transfers out		65
Securities transferred into or out of level 3, net	37
Assets, ending balance	9,481	9,025
Level 3 \| Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	5,253	13,898
Assets, earnings	609	(1,044)
Assets, other comprehensive income	0	0
Assets, Impairments	0	(7,601)
Assets, purchases	0	0
Assets, (sales)	(57)	0
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	5,805	5,253
Level 3 \| Common stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	1,558	2,599
Assets, earnings	611	(1,041)
Assets, other comprehensive income	0	0
Assets, Impairments	0	0
Assets, purchases	0	0
Assets, (sales)	0	0
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	2,169	1,558
Level 3 \| Preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	3,695	11,299
Assets, earnings	(2)	(3)
Assets, other comprehensive income	0	0
Assets, Impairments	0	(7,601)
Assets, purchases	0	0
Assets, (sales)	(57)	0
Assets, maturities	0	0
Assets. transfers out	0	0
Assets, ending balance	3,636	3,695
Level 3 \| Arbitrage trading account
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Assets, beginning balance	3,772	3,590
Assets, earnings	(133)	117
Assets, other comprehensive income	0	0
Assets, Impairments	0
Assets, Impairments		0
Assets, purchases	0	0
Assets, (sales)	0	0
Assets, maturities	0	0
Assets. transfers out		65
Securities transferred into or out of level 3, net	37
Assets, ending balance	$ 3,676	$ 3,772

Reserves for Loss and Loss Ex_3

Reserves for Loss and Loss Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves at beginning of period	$ 15,661,820	$ 14,248,879
Net provision for losses and loss expenses:
Claims occurring during the current year	1,647,674	1,502,817
Decrease in estimates for claims occurring in prior years	7,367	28,205
Loss reserve discount accretion	8,737	7,733
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	1,663,778	1,538,755
Net payments for claims:
Current year	107,434	110,274
Prior years	1,158,864	1,106,481
Total	1,266,298	1,216,755
Foreign currency translation	(52,944)	1,154
Net reserves at end of period	16,006,356	14,572,033	$ 15,661,820
Ceded reserves at end of period	3,093,272	2,859,602
Gross reserves at end of period	$ 19,099,628	$ 17,431,635	$ 18,739,652

Reserves for Loss and Loss Ex_4

Reserves for Loss and Loss Expenses (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Net of loss reserves discount	$ 14,000,000	$ 11,000,000
Increase (decrease) in estimates for claims	10,000,000	(19,000,000)
Adjustment expense	1,000,000	24,000,000
Liability recognized for best estimate net of reinsurance	386,000,000
Liability recognized for best estimate net of reinsurance, reported losses	383,000,000
Liability recognized for best estimate net of reinsurance, incurred but not reported (IBNR)	3,000,000
Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability recognized for best estimate net of reinsurance	328,000,000
Unfavorable reserve development net of premium offsets	8,000,000	12,000,000
Reinsurance & Monoline Excess
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability recognized for best estimate net of reinsurance	58,000,000
Unfavorable reserve development net of premium offsets		$ 12,000,000
Favorable reserve development net of premium offsets	$ 9,000,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Equity securities	$ 1,178,048	$ 1,090,347
Arbitrage trading account	1,146,000	938,000
Loans receivable	229,156	198,244
Carrying Value
Assets:
Fixed maturity securities	20,964,854	20,178,308
Equity securities	1,178,048	1,090,347
Arbitrage trading account	1,146,119	938,049
Loans receivable	228,766	201,271
Cash and cash equivalents	1,169,053	1,363,195
Trading account receivables from brokers and clearing organizations	141,277	303,614
Due from broker	0	36,747
Liabilities:
Due to broker	33,027	0
Trading account securities sold but not yet purchased	40,298	9,357
Senior notes and other debt	1,827,997	1,827,951
Subordinated debentures	1,009,269	1,009,090
Fair Value
Assets:
Fixed maturity securities	20,967,212	20,181,547
Equity securities	1,178,048	1,090,347
Arbitrage trading account	1,146,119	938,049
Loans receivable	229,156	198,244
Cash and cash equivalents	1,169,053	1,363,195
Trading account receivables from brokers and clearing organizations	141,277	303,614
Due from broker	0	36,747
Liabilities:
Due to broker	33,027	0
Trading account securities sold but not yet purchased	40,298	9,357
Senior notes and other debt	1,435,877	1,480,076
Subordinated debentures	$ 893,358	$ 929,598

Premiums and Reinsurance Rela_3

Premiums and Reinsurance Related Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Written premiums:
Written premiums, direct	$ 3,039,066	$ 2,738,754
Written premiums, assumed	323,689	310,563
Written premiums, ceded	(511,464)	(474,493)
Total net premiums written	2,851,291	2,574,824
Earned premiums:
Earned premiums, direct	2,936,643	2,667,063
Earned premiums, assumed	337,911	295,230
Earned premiums, ceded	(510,207)	(470,861)
Net premiums earned	2,764,347	2,491,432
Ceded losses and loss expenses incurred	305,951	315,476
Ceded commissions earned	$ 121,054	$ 118,418

Premiums and Reinsurance Rela_4

Premiums and Reinsurance Related Information - Premiums and Reinsurance, Allowance For Credit Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ 35,110	$ 30,660
Cumulative effect adjustment resulting from changes in accounting principles	35,039	32,353
Change in expected credit losses	(71)	1,693
Allowance for expected credit losses, end of period	35,039	32,353
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	8,404	8,064
Cumulative effect adjustment resulting from changes in accounting principles	9,185	8,703
Reinsurance Recoverable, Credit Loss Expense (Reversal)	781	639
Allowance for expected credit losses, end of period	$ 9,185	$ 8,703

Restricted Stock Units (Summary

Restricted Stock Units (Summary of Restricted Stock Units Issued) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Share based compensation expense	$ 13,000	$ 12,000
Restricted stock
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Restricted stock units (in units)	1,214	0
Fair Value	$ 100	$ 0
Minimum \| Restricted stock
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Award vesting period	3 years
Maximum \| Restricted stock
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Award vesting period	5 years

Leases (Lease Cost) (Details)

Leases (Lease Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
Leases (Lease Cost) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Leases [Abstract]
Lease cost	$ 11,077	$ 10,188
Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows	12,232	10,563
Right-of-use assets obtained in exchange for new lease liabilities	$ 24,695	$ 5,313

Leases (Supplemental Balance Sh

Leases (Supplemental Balance Sheet Information) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Leases [Abstract]
Operating lease, right-of-use asset	$ 191,720	$ 164,547
Operating lease, liability	$ 233,114	$ 199,225
Weighted-average remaining lease term	7 years 7 months 6 days	7 years 1 month 6 days
Weighted-average discount rate	5.44%	4.49%

Leases (Maturities of Operating

Leases (Maturities of Operating Lease Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Leases [Abstract]
2024	$ 38,862
2025	44,402
2026	37,499
2027	28,341
2028	26,760
Thereafter	104,223
Total undiscounted future minimum lease payments	280,087
Less: Discount impact	46,973
Total lease liability	$ 233,114	$ 199,225

Business Segments (Financial In

Business Segments (Financial Information of Company Operating Segments) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| segment	2
Segment Reporting Information [Line Items]
Earned Premiums (1)	$ 2,764,347	$ 2,491,432
Investment Income	319,839	223,398
Other	172,587	180,174
Total revenues	3,256,773	2,895,004
Pre-Tax Income (Loss)	574,071	376,071
Net Income (Loss) to Common Stockholders	442,471	294,126
Net investment gains	25,780	23,010
Net investment gains, net of tax	19,147	18,160
Corporate, other and eliminations
Segment Reporting Information [Line Items]
Earned Premiums (1)	0	0
Investment Income	21,850	5,257
Other	137,384	147,587
Total revenues	159,234	152,844
Pre-Tax Income (Loss)	(57,482)	(100,850)
Net Income (Loss) to Common Stockholders	(43,893)	(80,499)
Insurance
Segment Reporting Information [Line Items]
Earned Premiums (1)		2,142,924
Insurance \| Operating Segments
Segment Reporting Information [Line Items]
Earned Premiums (1)	2,398,768	2,142,924
Investment Income	244,778	163,558
Other	9,423	9,577
Total revenues	2,652,969	2,316,059
Pre-Tax Income (Loss)	478,149	352,626
Net Income (Loss) to Common Stockholders	365,091	274,108
Insurance \| Operating Segments \| Non-US
Segment Reporting Information [Line Items]
Total revenues	393,000	274,000
Reinsurance & Monoline Excess
Segment Reporting Information [Line Items]
Earned Premiums (1)		348,508
Reinsurance & Monoline Excess \| Operating Segments
Segment Reporting Information [Line Items]
Earned Premiums (1)	365,579	348,508
Investment Income	53,211	54,583
Other	0	0
Total revenues	418,790	403,091
Pre-Tax Income (Loss)	127,624	101,285
Net Income (Loss) to Common Stockholders	102,126	82,357
Reinsurance & Monoline Excess \| Operating Segments \| Non-US
Segment Reporting Information [Line Items]
Total revenues	111,000	106,000
Net investment gains
Segment Reporting Information [Line Items]
Earned Premiums (1)	0	0
Investment Income	$ 0	$ 0

Business Segments (Identifiable

Business Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 37,851,072	$ 37,111,830
Operating Segments \| Insurance
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	30,048,006	29,923,282
Operating Segments \| Reinsurance & Monoline Excess
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	5,506,533	5,545,249
Corporate Reconciling Items And Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 2,296,533	$ 1,643,299

Business Segments (Net Premiums

Business Segments (Net Premiums Earned By Major Line of Business) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenue from External Customer [Line Items]
Net premiums earned	$ 2,764,347	$ 2,491,432
Insurance
Revenue from External Customer [Line Items]
Net premiums earned		2,142,924
Insurance \| Operating Segments
Revenue from External Customer [Line Items]
Net premiums earned	2,398,768	2,142,924
Insurance \| Other liability
Revenue from External Customer [Line Items]
Net premiums earned	967,260	853,472
Insurance \| Short-tail lines
Revenue from External Customer [Line Items]
Net premiums earned	510,809	412,534
Insurance \| Auto
Revenue from External Customer [Line Items]
Net premiums earned	354,013	294,116
Insurance \| Workers' compensation
Revenue from External Customer [Line Items]
Net premiums earned	301,495	305,561
Insurance \| Professional liability
Revenue from External Customer [Line Items]
Net premiums earned	265,191	277,241
Reinsurance & Monoline Excess
Revenue from External Customer [Line Items]
Net premiums earned		348,508
Reinsurance & Monoline Excess \| Operating Segments
Revenue from External Customer [Line Items]
Net premiums earned	365,579	348,508
Reinsurance & Monoline Excess \| Casualty
Revenue from External Customer [Line Items]
Net premiums earned	197,844	214,712
Reinsurance & Monoline Excess \| Monoline excess
Revenue from External Customer [Line Items]
Net premiums earned	65,351	58,644
Reinsurance & Monoline Excess \| Property
Revenue from External Customer [Line Items]
Net premiums earned	$ 102,384	$ 75,152