Earnings per share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Basic weighted average number of shares outstanding	10,349,803	10,736,166	11,666,194
Net dilutive effect of share-based awards, treasury stock method (in shares)	880,204	909,542	941,558
Diluted weighted average number of shares outstanding	11,230,007	11,645,708	12,607,752
Net income attributable to Oppenheimer Holdings Inc.	$ 71,557	$ 30,179	$ 32,351
Basic (in dollars per share)	$ 6.91	$ 2.81	$ 2.77
Diluted (in dollars per share)	$ 6.37	$ 2.59	$ 2.57
Class A Stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Number of anti-dilutive stock options granted	0	115,950	4,100