Consolidated Statements of Operations - USD ($) $ 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
REVENUE
Commissions									$ 329,668	$ 336,620	$ 377,317
Investment Advisory Fee Revenue									314,349	320,746	269,119
Investment banking									115,353	78,215	81,011
Interest Income, Deposits with Financial Institutions									116,052	76,839	36,316
Interest									52,484	48,498	47,649
Principal transactions, net									14,461	23,273	20,481
Other									15,787	36,147	25,886
Total revenue	$ 243,254	$ 237,814	$ 242,556	$ 234,530	$ 264,973	$ 226,220	$ 215,884	$ 213,261	958,154	920,338	857,779
EXPENSES
Compensation and related expenses									607,192	602,138	584,710
Communications and technology									74,479	71,978	70,390
Occupancy and equipment costs									61,171	61,164	60,791
Clearing and exchange fees									22,985	23,545	25,126
Interest									46,396	28,354	19,437
Other									101,078	113,423	119,217
Total 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)
Current and Deferred Income Tax Expense (Benefit) from Continuing Operations									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)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax									0	2,071	17,339
Discontinued Operation, Tax Effect of Discontinued Operation									0	941	7,218
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)
Basic net income (loss) per share attributable to Oppenheimer Holdings Inc.
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)
Dividends	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.44	$ 0.44	$ 440.00
Weighted average shares
Basic									13,248,876	13,246,423	13,368,768
Diluted									14,061,369	13,673,361	13,368,768
Retained Earnings [Member]
EXPENSES
Net income (loss) attributable to Oppenheimer Holdings Inc.									$ 28,892	$ 22,816	$ (1,161)
Basic net income (loss) per share attributable to Oppenheimer Holdings Inc.
Dividends									$ 0.44	$ 0.44	$ 0.44