Earnings Per Share - Summary of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding										13,246,423	13,368,768	13,640,610
Net dilutive effect of share-based awards, treasury method	[1]									426,938	0	0
Diluted weighted average number of shares outstanding										13,673,361	13,368,768	13,640,610
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		$ 21,168	$ 7,403	$ (1,363)	$ (5,338)	$ (2,424)	$ (1,059)	$ (2,855)	$ (3,292)	$ 21,870	$ (9,630)	$ (2,834)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		29	461	53	587	759	413	9,566	(617)	1,130	10,121	5,732
Net income		21,197	7,864	(1,310)	(4,751)	(1,665)	(646)	6,711	(3,909)	23,000	491	2,898
Net income attributable to non-controlling interest, net of tax		4	75	9	96	125	66	1,523	(62)	184	1,652	936
Net income (loss) attributable to Oppenheimer Holdings Inc.		$ 21,193	$ 7,789	$ (1,319)	$ (4,847)	$ (1,790)	$ (712)	$ 5,188	$ (3,847)	$ 22,816	$ (1,161)	$ 1,962
Income (Loss) from Continuing Operations, Per Basic Share		$ 1.61	$ 0.56	$ (0.10)	$ (0.40)	$ (0.28)	$ (0.08)	$ (0.21)	$ (0.25)	$ 1.65	$ (0.72)	$ (0.21)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share		0.00	0.03	0.00	0.04	0.05	0.03	0.60	(0.04)	0.07	0.63	0.35
Net income (loss) per share		1.61	0.59	(0.10)	(0.36)	0	0	0	0	1.72	(0.09)	0.14
Income (Loss) from Continuing Operations, Per Diluted Share		1.54	0.54	(0.10)	(0.40)	(0.28)	(0.08)	(0.21)	(0.25)	1.60	(0.72)	(0.21)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share		0.00	0.03	0.00	0.04	0.05	0.03	0.60	(0.04)	0.07	0.63	0.35
Diluted earnings per share		$ 1.54	$ 0.57	$ (0.10)	$ (0.36)	$ 0	$ 0	$ 0	$ 0	$ 1.67	$ (0.09)	$ 0.14

[1] For the year ended December 31, 2017, the diluted earnings per share computation does not include the anti-dilutive effect of 10,592 shares of Class A Stock granted under share-based compensation arrangements (1,237,134 and 1,269,585 shares for the years ended December 31, 2016 and 2015, respectively).(2)Represents net income from discontinued operations less net income attributable to noncontrolling interest, net of tax divided by weighted average number of shares outstanding.