Condensed Consolidating Financial Information - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
REVENUES
Commissions	$ 77,635	$ 90,023	$ 248,204	$ 286,447
Advisory fees	74,329	67,452	216,521	199,582
Investment banking	23,940	20,280	57,347	51,544
Interest	12,952	11,291	36,346	36,340
Principal transactions, net	5,135	4,922	15,810	19,117
Other	32,229	17,836	81,137	45,804
Total revenue	226,220	211,804	655,365	638,834
EXPENSES
Compensation and related expenses	142,090	142,308	428,625	432,524
Communications and technology	17,781	17,201	53,886	52,519
Occupancy and equipment costs	15,288	14,909	45,721	44,796
Clearing and exchange fees	5,622	5,886	17,392	19,006
Interest	6,500	4,687	18,710	14,526
Other	27,111	28,623	87,865	89,859
Total expenses	214,392	213,614	652,199	653,230
Income (Loss) before income taxes	11,828	(1,810)	3,166	(14,396)
Income taxes	4,425	(751)	2,464	(7,190)
Net income (loss) from continuing operations	7,403	(1,059)	702	(7,206)
Income attributable to noncontrolling interest before income taxes	769	888	1,834	15,597
Tax effect of discontinued operation	308	475	733	6,235
Net income from discontinued operations	461	413	1,101	9,362
Equity in earnings of subsidiaries	0	0	0	0
Net income	7,864	(646)	1,803	2,156
Net income attributable to noncontrolling interest, net of tax	75	66	180	1,527
Net income (loss) attributable to Oppenheimer Holdings Inc.	7,789	(712)	1,623	629
Other comprehensive income (loss)	(251)	681	1,953	900
Comprehensive income (loss) attributable to Oppenheimer Holdings Inc.	7,538	(31)	3,576	1,529
Eliminations [Member]
REVENUES
Commissions	0	0	0	0
Advisory fees	(326)	(437)	(989)	(1,197)
Investment banking	0	0	(3,000)	0
Interest	(2,411)	(2,692)	(7,562)	(7,824)
Principal transactions, net	0	0	0	0
Other	(89)	(81)	(266)	(239)
Total revenue	(2,826)	(3,210)	(11,817)	(9,260)
EXPENSES
Compensation and related expenses	0	0	0	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	(89)	(81)	(266)	(239)
Clearing and exchange fees	0	0	0	0
Interest	(2,411)	(2,692)	(7,562)	(7,824)
Other	(326)	(437)	(3,989)	(1,197)
Total expenses	(2,826)	(3,210)	(11,817)	(9,260)
Income (Loss) before income taxes	0	0	0	0
Income taxes	0	0	0	0
Net income (loss) from continuing operations	0	0	0	0
Income attributable to noncontrolling interest before income taxes	0	0	0	0
Tax effect of discontinued operation	0	0	0	0
Net income from discontinued operations	0	0	0	0
Equity in earnings of subsidiaries	(19,164)	(51)	(18,438)	(6,573)
Net income	(19,164)	(51)	(18,438)	(6,573)
Net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	(19,164)	(51)	(18,438)	(6,573)
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss) attributable to Oppenheimer Holdings Inc.	(19,164)	(51)	(18,438)	(6,573)
Parent Company [Member]
REVENUES
Commissions	0	0	0	0
Advisory fees	0	0	0	0
Investment banking	0	0	0	0
Interest	0	0	0	0
Principal transactions, net	0	0	0	0
Other	22	0	22	0
Total revenue	22	0	22	0
EXPENSES
Compensation and related expenses	271	251	976	994
Communications and technology	33	30	112	92
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	3,375	3,281	10,365	9,844
Other	412	310	4,661	1,506
Total expenses	4,091	3,872	16,114	12,436
Income (Loss) before income taxes	(4,069)	(3,872)	(16,092)	(12,436)
Income taxes	(1,558)	(2,018)	(6,184)	(7,004)
Net income (loss) from continuing operations	(2,511)	(1,854)	(9,908)	(5,432)
Income attributable to noncontrolling interest before income taxes	0	0	0	0
Tax effect of discontinued operation	0	0	0	0
Net income from discontinued operations	0	0	0	0
Equity in earnings of subsidiaries	10,300	1,142	11,531	6,061
Net income	7,789	(712)	1,623	629
Net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	7,789	(712)	1,623	629
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss) attributable to Oppenheimer Holdings Inc.	7,789	(712)	1,623	629
Guarantor Subsidiaries [Member]
REVENUES
Commissions	0	0	0	0
Advisory fees	0	0	0	0
Investment banking	0	0	0	0
Interest	2,391	2,556	7,529	7,669
Principal transactions, net	2	1	17	53
Other	89	81	267	240
Total revenue	2,482	2,638	7,813	7,962
EXPENSES
Compensation and related expenses	0	0	0	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	0	0	0	0
Other	62	3	329	8
Total expenses	62	3	329	8
Income (Loss) before income taxes	2,420	2,635	7,484	7,954
Income taxes	984	402	2,860	2,405
Net income (loss) from continuing operations	1,436	2,233	4,624	5,549
Income attributable to noncontrolling interest before income taxes	0	0	0	0
Tax effect of discontinued operation	0	0	0	0
Net income from discontinued operations	0	0	0	0
Equity in earnings of subsidiaries	8,864	(1,091)	6,907	512
Net income	10,300	1,142	11,531	6,061
Net income attributable to noncontrolling interest, net of tax	0	0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	10,300	1,142	11,531	6,061
Other comprehensive income (loss)	0	0	0	0
Comprehensive income (loss) attributable to Oppenheimer Holdings Inc.	10,300	1,142	11,531	6,061
Non-Guarantor Subsidiaries [Member]
REVENUES
Commissions	77,635	90,023	248,204	286,447
Advisory fees	74,655	67,889	217,510	200,779
Investment banking	23,940	20,280	60,347	51,544
Interest	12,972	11,427	36,379	36,495
Principal transactions, net	5,133	4,921	15,793	19,064
Other	32,207	17,836	81,114	45,803
Total revenue	226,542	212,376	659,347	640,132
EXPENSES
Compensation and related expenses	141,819	142,057	427,649	431,530
Communications and technology	17,748	17,171	53,774	52,427
Occupancy and equipment costs	15,377	14,990	45,987	45,035
Clearing and exchange fees	5,622	5,886	17,392	19,006
Interest	5,536	4,098	15,907	12,506
Other	26,963	28,747	86,864	89,542
Total expenses	213,065	212,949	647,573	650,046
Income (Loss) before income taxes	13,477	(573)	11,774	(9,914)
Income taxes	4,999	865	5,788	(2,591)
Net income (loss) from continuing operations	8,478	(1,438)	5,986	(7,323)
Income attributable to noncontrolling interest before income taxes	769	888	1,834	15,597
Tax effect of discontinued operation	308	475	733	6,235
Net income from discontinued operations	461	413	1,101	9,362
Equity in earnings of subsidiaries	0	0	0	0
Net income	8,939	(1,025)	7,087	2,039
Net income attributable to noncontrolling interest, net of tax	75	66	180	1,527
Net income (loss) attributable to Oppenheimer Holdings Inc.	8,864	(1,091)	6,907	512
Other comprehensive income (loss)	(251)	681	1,953	900
Comprehensive income (loss) attributable to Oppenheimer Holdings Inc.	$ 8,613	$ (410)	$ 8,860	$ 1,412