Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding (in shares)	10,327,818	11,016,430	10,367,636	11,054,306
Net dilutive effect of share-based awards, treasury stock method (in shares)	784,085	0	715,786	857,073
Diluted weighted average number of shares outstanding (in shares)	11,111,903	11,016,430	11,083,422	11,911,379
Net income attributable to Oppenheimer Holdings Inc.	$ 10,266	$ (9,400)	$ 36,320	$ 5,217
Earnings per share attributable to Oppenheimer Holdings Inc. - Basic (in dollars per share)	$ 0.99	$ (0.85)	$ 3.49	$ 0.47
Earnings per share attributable to Oppenheimer Holdings Inc. - Diluted (in dollars per share)	$ 0.92	$ (0.85)	$ 3.29	$ 0.44
Class A Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive stock options granted (in shares)	0	1,138,992	1,000	281,810