Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding (in shares)	10,407,454	11,092,603
Net dilutive effect of share-based awards, treasury stock method (in shares)	594,215	870,889
Diluted weighted average number of shares outstanding (in shares)	11,001,669	11,963,492
Net income attributable to Oppenheimer Holdings Inc.	$ 26,054	$ 14,617
Earnings per share attributable to Oppenheimer Holdings Inc., Basic (in dollars per share)	$ 2.50	$ 1.32
Earnings per share attributable to Oppenheimer Holdings Inc., Diluted (in dollars per share)	$ 2.37	$ 1.22
Class A Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive stock options granted (in shares)		282,360