Quarterly Information - Schedule of Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 295,881	$ 234,793	$ 250,935	$ 251,770	$ 243,254		$ 237,814		$ 242,556		$ 234,530		$ 1,033,379		$ 958,154		$ 920,338
Operating Expenses	260,908	228,297	233,544	235,718	227,677		230,660		230,039		224,909		958,467		913,285		900,786
Income (loss) before income taxes from continuing operations	34,973	6,496	17,391	16,052	15,577		7,154		12,517		9,621		74,912		44,869		19,552
Other Income Tax Expense (Benefit), Continuing Operations	9,538	2,547	5,016	4,858	7,316		2,083		3,662		2,916		21,959		15,977		(2,134)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest													52,953		28,892		21,686
Net income (loss) attributable to Oppenheimer Holdings Inc.	$ 25,435	$ 3,949	$ 12,375	$ 11,194	$ 8,261		$ 5,071		$ 8,855		$ 6,705		$ 52,953		$ 28,892		$ 22,816
Income (Loss) from Continuing Operations, Per Basic Share													$ 4.10		$ 2.18		$ 1.65
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share													0.00		0.00		0.07
Net income per share	$ 1.99	$ 0.31	$ 0.95	$ 0.86	$ 0.62		$ 0.38		$ 0.67		$ 0.51		4.10		2.18		1.72
Income (Loss) from Continuing Operations, Per Diluted Share													3.82		2.05		1.60
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share													0.00		0.00		0.07
Earnings Per Share, Diluted	1.83	0.29	0.89	0.81	0.59		0.36		0.63		0.48		3.82		2.05		$ 1.67
Dividends paid per share	$ 0.12	0.12	0.11	0.11	0.11		0.11		0.11		0.11		0.46		0.44
Market price of Class A Stock
High		31.30	27.42	28.73	33.76	[1]	34.15	[1]	29.8	[1]	29	[1]	31.3	[2]	34.15	[1]
Low		$ 26.42	$ 24.34	$ 25.25	$ 23.52	[1]	$ 27.4	[1]	$ 24.6	[1]	$ 25.25	[1]	$ 24.34	[2]	$ 23.52	[1]

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