Earnings per share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Basic weighted average number of shares outstanding	10,502,853	10,349,803	10,736,166
Net dilutive effect of share-based awards, treasury stock method (in shares)	880,387	880,204	909,542
Diluted weighted average number of shares outstanding	11,383,240	11,230,007	11,645,708
Net income attributable to Oppenheimer Holdings Inc.	$ 148,403	$ 71,557	$ 30,179
Basic (in dollars per share)	$ 14.13	$ 6.91	$ 2.81
Diluted (in dollars per share)	$ 13.04	$ 6.37	$ 2.59
Class A Stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Number of anti-dilutive stock options granted	6,500	0	115,950