Quarterly Information - Schedule of Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 243,254	$ 237,814	$ 242,556	$ 234,530	$ 264,973		$ 226,220		$ 215,884		$ 213,261		$ 958,154		$ 920,338		$ 857,779
Operating Expenses	227,671	230,670	230,055	224,905	248,403		214,392		217,521		220,286		913,301		900,602		879,671
Income (loss) before income taxes from continuing operations	15,583	7,144	12,501	9,625	16,570		11,828		(1,637)		(7,025)		44,853		19,736		(21,892)
Other Income Tax Expense (Benefit), Continuing Operations	7,316	2,083	3,662	2,916	(4,598)		4,425		(274)		(1,687)		15,977		(2,134)		(12,262)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	8,267	5,061	8,839	6,709	21,168		7,403		(1,363)		(5,338)		28,876		21,870		(9,630)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	0	0	0	0	29		461		53		587		0		1,130		10,121
Net income	8,267	5,061	8,839	6,709	21,197		7,864		(1,310)		(4,751)		28,876		23,000		491
Less net income (loss) attributable to non-controlling interest, net of tax	6	(10)	(16)	4	4		75		9		96		(16)		184		1,652
Net income (loss) attributable to Oppenheimer Holdings Inc.	$ 8,261	$ 5,071	$ 8,855	$ 6,705	$ 21,193		$ 7,789		$ (1,319)		$ (4,847)		$ 28,892		$ 22,816		$ (1,161)
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.62	$ 0.38	$ 0.67	$ 0.51	$ 1.61		$ 0.56		$ (0.10)		$ (0.40)		$ 2.18		$ 1.65		$ (0.72)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.00	0.00	0.00	0.00	0.00		0.03		0.00		0.04		0.00		0.07		0.63
Net income (loss) per share	0.62	0.38	0.67	0.51	2		1		0		0		2.18		1.72		(0.09)
Income (Loss) from Continuing Operations, Per Diluted Share	0.59	0.36	0.63	0.48	1.54		0.54		(0.10)		(0.40)		2.05		1.60		(0.72)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0.00	0.00	0.00	0.00	0.00		0.03		0.00		0.04		0.00		0.07		0.63
Earnings Per Share, Diluted	0.59	0.36	0.63	0.48	2		1		0		0		2.05		1.67		(0.09)
Basic net income 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		0.44		0.44		$ 440.00
Market price of Class A Stock
High					29	[1]	17.70	[1]	18.25	[1]	19.60	[1]	34.15	[2]	29	[1]
Low					$ 17.35	[1]	$ 15.40	[1]	$ 15.10	[1]	$ 15.90	[1]	$ 23.52	[2]	$ 15.1	[1]

[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.