Document and Entity Information - shares	3 Months Ended
	Jun. 30, 2025	Aug. 14, 2025
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
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2025
Amendment Flag	false
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	Q1
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 Street
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	531
Local Phone Number	867-3631
Title of 12(b) Security	Common Stock
Trading Symbol	OMCC
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		6,753,625