Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding (in shares)	10,332,927	10,519,431	10,355,982	10,874,055
Net dilutive effect of share-based awards, treasury stock method (in shares)	944,938	920,798	800,554	872,282
Diluted weighted average number of shares outstanding (in shares)	11,277,865	11,440,229	11,156,536	11,746,337
Net income attributable to Oppenheimer Holdings Inc.	$ 24,508	$ 13,861	$ 60,828	$ 19,079
Earnings per share attributable to Oppenheimer Holdings Inc. - Basic (in dollars per share)	$ 2.38	$ 1.32	$ 5.87	$ 1.75
Earnings per share attributable to Oppenheimer Holdings Inc. - Diluted (in dollars per share)	$ 2.16	$ 1.21	$ 5.45	$ 1.62
Class A Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive stock options granted (in shares)	0	286,185	0	277,435