Earnings per share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Basic weighted average number of shares outstanding	10,736,166	11,666,194	12,642,306
Net dilutive effect of share-based awards, treasury stock method (in shares)	909,542	941,558	940,522
Diluted weighted average number of shares outstanding	11,645,708	12,607,752	13,582,828
Net income attributable to Oppenheimer Holdings Inc.	$ 30,179	$ 32,351	$ 158,964
Basic (in dollars per share)	$ 2.81	$ 2.77	$ 12.57
Diluted (in dollars per share)	$ 2.59	$ 2.57	$ 11.70
Class A Stock
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Number of anti-dilutive stock options granted	115,950	4,100