Some of our material subsidiaries (the “Guarantors”) have guaranteed the obligations of the borrowers under the Credit Agreement, subject to certain exceptions. The borrowers’ obligations under the Credit Agreement are secured by a lien on substantially all of our assets and the Guarantors’ assets, subject to certain exceptions.
The Credit Agreement contains customary negative covenants that include, among other things, limitations on our and certain of our subsidiaries’ ability, subject to certain exceptions, to incur liens and debt, make investments, dispositions, and restricted payments, change the nature of our business, consummate mergers, consolidations and the sale of all or substantially all of our respective assets, taken as a whole, and transact with affiliates. We are also required to maintain a consolidated interest coverage ratio of at least 3.00 to 1.00 and a consolidated leverage ratio of less than or equal to 4.00 to 1.00 (subject to certain adjustments in connection with permitted acquisitions), tested on a quarterly basis (the “Financial Covenants”). The Financial Covenants do not apply to the Term B Facility. Our consolidated leverage ratio was 2.00 to 1.00 at December 31, 2023. As of December 31, 2023, we were in compliance with the covenants of the Credit Agreement.
The Credit Agreement contains customary affirmative covenants, including, among other things, compliance with applicable law, preservation of existence, maintenance of properties and of insurance, and keeping proper books and records. The Credit Agreement contains customary events of default, including, among other things, nonpayment of principal, interest or fees, cross-defaults to other debt, inaccuracies of representations and warranties, failure to perform covenants, events of bankruptcy and insolvency, change of control and unsatisfied judgments, subject in certain cases to notice and cure periods and other exceptions.
At December 31, 2023 and September 30, 2023, letters of credit totaled $4.4 million and $4.4 million, respectively, under our Revolving Credit Facility. As of December 31, 2023 and September 30, 2023, we had $1,145.6 million and $1,145.6 million, respectively, available under our revolving credit facility.
2027 Senior Notes
On February 21, 2017, we completed a private placement offering of $1,000,000,000 aggregate principal amount of our unsecured 5.125% Senior Notes due 2027 (the “2027 Senior Notes”). On June 30, 2017, we completed an exchange offer to exchange the unregistered 2027 Senior Notes for registered notes, as well as related guarantees.
As of December 31, 2023, the estimated fair value of the 2027 Senior Notes was approximately $979.8 million. The fair value of the 2027 Senior Notes as of December 31, 2023 was derived by taking the mid-point of the trading prices from an observable market input (Level 2) in the secondary bond market and multiplying it by the outstanding balance of the 2027 Senior Notes. Interest is payable on the 2027 Senior Notes at a rate of 5.125% per annum. Interest on the 2027 Senior Notes is payable semi-annually on March 15 and September 15 of each year, commencing on September 15, 2017. The 2027 Senior Notes will mature on March 15, 2027.
At any time and from time to time prior to December 15, 2026, we may redeem all or part of the 2027 Senior Notes, at a redemption price equal to 100% of their principal amount, plus a “make whole” premium as of the redemption date, and accrued and unpaid interest to the redemption date. On or after December 15, 2026, we may redeem all or part of the 2027 Senior Notes at a redemption price equal to 100% of their principal amount, plus accrued and unpaid interest on the redemption date.
The indenture pursuant to which the 2027 Senior Notes were issued contains customary events of default, including, among other things, payment default, exchange default, failure to provide notices thereunder and provisions related to bankruptcy events. The indenture also contains customary negative covenants.
We were in compliance with the covenants relating to the 2027 Senior Notes as of December 31, 2023.
Other Debt and Other Items
Other debt consists primarily of obligations under capital leases and loans, and unsecured credit facilities. The unsecured credit facilities are primarily used for standby letters of credit issued in connection with general and professional liability insurance programs and for contract performance guarantees. At December 31, 2023 and September 30, 2023, these outstanding standby letters of credit totaled $887.6 million and $878.9 million, respectively. As of December 31, 2023, we had $406.1 million available under these unsecured credit facilities.