Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive stock options granted (in shares)				1,000
Basic weighted average number of shares outstanding (in shares)	10,520,219	10,327,818	10,493,145	10,367,636
Net dilutive effect of share-based awards, treasury stock method (in shares)	828,830	784,085	815,834	715,786
Diluted weighted average number of shares outstanding (in shares)	11,349,049	11,111,903	11,308,979	11,083,422
Net income attributable to Oppenheimer Holdings Inc.	$ 21,674	$ 10,266	$ 52,329	$ 36,320
Earnings per share attributable to Oppenheimer Holdings Inc. - Basic (in dollars per share)	$ 2.06	$ 0.99	$ 4.99	$ 3.49
Earnings per share attributable to Oppenheimer Holdings Inc. - Diluted (in dollars per share)	$ 1.91	$ 0.92	$ 4.63	$ 3.29
Class A Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive stock options granted (in shares)	199,850	0	202,475