Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Basic weighted average number of shares outstanding (in shares)	10,519,722	10,332,927	10,502,101	10,355,982
Net dilutive effect of share-based awards, treasury stock method (in shares)	930,624	944,938	847,700	800,554
Diluted weighted average number of shares outstanding (in shares)	11,450,346	11,277,865	11,349,801	11,156,536
Net income attributable to Oppenheimer Holdings Inc.	$ 21,712	$ 24,508	$ 74,041	$ 60,828
Earnings per share attributable to Oppenheimer Holdings Inc. - Basic (in dollars per share)	$ 2.06	$ 2.38	$ 7.05	$ 5.87
Earnings per share attributable to Oppenheimer Holdings Inc. - Diluted (in dollars per share)	$ 1.90	$ 2.16	$ 6.53	$ 5.45
Class A Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive stock options granted (in shares)	7,000	0	8,000	0