Earnings Per Share - Summary of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding		13,269,024	13,213,139	13,252,596	13,290,399
Net dilutive effect of share-based awards, treasury method	[1]	871,239	550,377	790,730	499,737
Diluted weighted average number of shares outstanding		14,140,263	13,763,516	14,043,326	13,790,136
Net income from continuing operations		$ 5,061	$ 7,403	$ 20,609	$ 702
Net income from discontinued operations		0	461	0	1,101
Net income		5,061	7,864	20,609	1,803
Net income attributable to non-controlling interest, net of tax		(10)	75	(22)	180
Net income attributable to Oppenheimer Holdings Inc.		$ 5,071	$ 7,789	$ 20,631	$ 1,623
Continuing operations (in dollars per share)		$ 0.38	$ 0.56	$ 1.56	$ 0.05
Discontinued operations (in dollars per share)		0.00	0.03	0.00	0.07
Net income per share		0.38	0.59	1.56	0.12
Continuing operations (in dollars per share)		0.36	0.54	1.47	0.05
Discontinued operations (in dollars per share)		0.00	0.03	0.00	0.07
Net loss per share (in dollars per share)		$ 0.36	$ 0.57	$ 1.47	$ 0.12

[1] For both the three and nine months ended September 30, 2018, the diluted net income per share computation does not include the anti-dilutive effect of 4,050 shares of Class A Stock granted under share-based compensation arrangements (15,450 shares for both the three and nine months ended September 30, 2017).(2)Represents net income from discontinued operations less net income attributable to non-controlling interest, net of tax divided by weighted average number of shares outstanding.