Quarterly Information - Schedule of Quarterly Information (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
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 264,973		$ 226,220		$ 215,884		$ 213,261		$ 218,945		$ 211,804		$ 212,074		$ 214,956		$ 920,338		$ 857,779		$ 897,801
Operating Expenses	248,403		214,392		217,521		220,286		226,441		213,614		217,320		222,296		900,602		879,671		900,229
Income (loss) before income taxes from continuing operations	16,570		11,828		(1,637)		(7,025)		(7,496)		(1,810)		(5,246)		(7,340)		19,736		(21,892)		(2,428)
Other Income Tax Expense (Benefit), Continuing Operations	(4,598)		4,425		(274)		(1,687)		(5,072)		(751)		(2,391)		(4,048)		(2,134)		(12,262)		406
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
Less net income attributable to noncontrolling 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
Earnings Per Share, Diluted	1.54		0.57		(0.10)		(0.36)		0		0		0		0		1.67		(0.09)		0.14
Basic net income (loss) per share attributable to Oppenheimer Holdings Inc.
Dividends per share	0.11		0.11		0.11		0.11		0.11		0.11		0.11		0.11		0.44000		0.44		$ 440.00
Market price of Class A Stock
High	29	[1]	17.70	[1]	18.25	[1]	19.60	[1]	19.65	[2]	16.49	[2]	16.66	[2]	16.98	[2]	29	[1]	19.65	[2]
Low	$ 17.35	[1]	$ 15.40	[1]	$ 15.10	[1]	$ 15.90	[1]	$ 13.65	[2]	$ 13.74	[2]	$ 13.63	[2]	$ 13.58	[2]	$ 15.1	[1]	$ 13.58	[2]

[1] The price quotations above were obtained from the New York Stock Exchange website.

[2] The price quotations above were obtained from the New York Stock Exchange website.