| Document and Entity Information - shares shares in Millions | 6 Months Ended | |
| Sep. 30, 2024 | Nov. 06, 2024 | |
| Cover [Abstract] | ||
| Entity Registrant Name | OLD MARKET CAPITAL CORPORATION | |
| Entity Central Index Key | 0001000045 | |
| Entity Current Reporting Status | Yes | |
| Current Fiscal Year End Date | --03-31 | |
| Entity Filer Category | Non-accelerated Filer | |
| Document Type | 10-Q/A | |
| Document Quarterly Report | true | |
| Document Transition Report | false | |
| Document Period End Date | Sep. 30, 2024 | |
| Amendment Flag | true | |
| Document Fiscal Year Focus | 2024 | |
| Document Fiscal Period Focus | Q2 | |
| Entity Small Business | true | |
| Entity Emerging Growth Company | false | |
| Entity Shell Company | false | |
| Entity Interactive Data Current | Yes | |
| Entity File Number | 0-26680 | |
| Entity Incorporation, State or Country Code | DE | |
| Entity Tax Identification Number | 59-2506879 | |
| Entity Address, Address Line One | 1601 Dodge St. | |
| Entity Address, Address Line Two | Suite 3350 | |
| Entity Address, City or Town | Omaha | |
| Entity Address, State or Province | NE | |
| Entity Address, Postal Zip Code | 68102 | |
| City Area Code | 727 | |
| Local Phone Number | 726-0763 | |
| Title of 12(b) Security | Common Stock | |
| Trading Symbol | OMCC | |
| Security Exchange Name | NASDAQ | |
| Entity Common Stock, Shares Outstanding | 6.7 | |
| Amendment Description | The purpose of this Amendment No. 1 (this “Amendment”) to our Quarterly Report on Form 10-Q for the period ended September 30, 2024 (the “Form 10-Q”), as filed with the Securities and Exchange Commission (the “SEC”) on November 13, 2024, is solely to correct errors in the number of outstanding shares of the Registrant’s common stock on the cover page of the Form 10-Q and in the Condensed Consolidated Balance Sheets.This Amendment makes no other changes to the Form 10-Q as filed with the SEC on November 13, 2024 and no attempt has been made in this Amendment to modify or update the other disclosures presented in the Form 10-Q. This Amendment does not reflect subsequent events occurring after the original filing of the Form 10-Q (those events occurring after November 13, 2024) or modify or update in any way those disclosures that may be affected by subsequent events. Accordingly, this Amendment should be read in conjunction with the Form 10-Q and our other filings with the SEC. |
| Insider Trading Arrangements | 3 Months Ended |
| Sep. 30, 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 |
