Earnings per share - Summary of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding (in shares)	11,980,115	12,689,191	12,222,527	12,634,464
Net dilutive effect of share-based awards, treasury method (in shares)	0	991,955	919,011	861,125
Diluted weighted average number of shares outstanding (in shares)	11,980,115	13,681,146	13,141,538	13,495,589
Net income (loss) attributable to Oppenheimer Holdings Inc.	$ (3,874)	$ 31,159	$ 5,418	$ 69,817
Basic (in dollars per share)	$ (0.32)	$ 2.46	$ 0.44	$ 5.53
Diluted (in dollars per share)	$ (0.32)	$ 2.28	$ 0.41	$ 5.17