Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
REVENUES
Commissions	$ 83,407	$ 86,717
Advisory fees	77,548	69,409
Investment banking	28,210	18,021
Sweep Interest Income from FDIC-Insured Bank Deposits	25,297	14,126
Interest	12,227	10,565
Principal transactions, net	2,726	5,373
Other	5,115	9,050
Total revenue	234,530	213,261
EXPENSES
Compensation and related expenses	153,104	143,878
Communications and technology	18,688	17,706
Occupancy and equipment costs	15,428	15,272
Clearing and exchange fees	6,096	5,854
Interest	8,963	5,356
Other	22,626	32,220
Total expenses	224,905	220,286
Income (Loss) before income taxes from continuing operations	9,625	(7,025)
Income Tax Expense (Benefit)	2,916	(1,687)
Net income (loss) from continuing operations	6,709	(5,338)
Income from discontinued operations	0	976
Equity in earnings of subsidiaries	0	0
Net income (loss)	6,709	(4,751)
Income taxes	0	389
Net income from discontinued operations	0	587
Less net income attributable to non-controlling interest, net of tax	4	96
Net income (loss) attributable to Oppenheimer Holdings Inc.	6,705	(4,847)
Other comprehensive loss	(142)	1,424
Total comprehensive income	6,563	(3,423)
Eliminations
REVENUES
Commissions	0	0
Advisory fees	(326)	(320)
Investment banking	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0
Interest	(2,080)	(2,576)
Principal transactions, net	(33)	0
Other	(95)	(88)
Total revenue	(2,534)	(2,984)
EXPENSES
Compensation and related expenses	0	0
Communications and technology	0	0
Occupancy and equipment costs	(95)	(88)
Clearing and exchange fees	0	0
Interest	(2,080)	(2,576)
Other	(359)	(320)
Total expenses	(2,534)	(2,984)
Income (Loss) before income taxes from continuing operations	0	0
Income Tax Expense (Benefit)	0	0
Net income (loss) from continuing operations	0	0
Income from discontinued operations		0
Equity in earnings of subsidiaries	(17,945)	6,479
Net income (loss)	(17,945)	6,479
Income taxes		0
Net income from discontinued operations		0
Less net income attributable to non-controlling interest, net of tax	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	(17,945)	6,479
Other comprehensive loss	0	0
Total comprehensive income	(17,945)	6,479
Guarantor Subsidiaries
REVENUES
Commissions	0	0
Advisory fees	0	0
Investment banking	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0
Interest	2,060	2,579
Principal transactions, net	0	6
Other	96	88
Total revenue	2,156	2,673
EXPENSES
Compensation and related expenses	0	0
Communications and technology	0	0
Occupancy and equipment costs	0	0
Clearing and exchange fees	0	0
Interest	0	0
Other	253	72
Total expenses	253	72
Income (Loss) before income taxes from continuing operations	1,903	2,601
Income Tax Expense (Benefit)	264	920
Net income (loss) from continuing operations	1,639	1,681
Income from discontinued operations		0
Equity in earnings of subsidiaries	8,153	(4,080)
Net income (loss)	9,792	(2,399)
Income taxes		0
Net income from discontinued operations		0
Less net income attributable to non-controlling interest, net of tax	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	9,792	(2,399)
Other comprehensive loss	0	0
Total comprehensive income	9,792	(2,399)
Non-Guarantor Subsidiaries
REVENUES
Commissions	83,407	86,717
Advisory fees	77,874	69,729
Investment banking	28,210	18,021
Sweep Interest Income from FDIC-Insured Bank Deposits	25,297	14,126
Interest	12,247	10,562
Principal transactions, net	2,759	5,367
Other	5,114	9,050
Total revenue	234,908	213,572
EXPENSES
Compensation and related expenses	152,778	143,540
Communications and technology	18,649	17,676
Occupancy and equipment costs	15,523	15,360
Clearing and exchange fees	6,096	5,854
Interest	7,668	4,651
Other	22,345	32,141
Total expenses	223,059	219,222
Income (Loss) before income taxes from continuing operations	11,849	(5,650)
Income Tax Expense (Benefit)	3,692	(1,079)
Net income (loss) from continuing operations	8,157	(4,571)
Income from discontinued operations		976
Equity in earnings of subsidiaries	0	0
Net income (loss)	8,157	(3,984)
Income taxes		389
Net income from discontinued operations		587
Less net income attributable to non-controlling interest, net of tax	4	96
Net income (loss) attributable to Oppenheimer Holdings Inc.	8,153	(4,080)
Other comprehensive loss	(142)	1,424
Total comprehensive income	8,011	(2,656)
Parent
REVENUES
Commissions	0	0
Advisory fees	0	0
Investment banking	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0
Interest	0	0
Principal transactions, net	0	0
Other	0	0
Total revenue	0	0
EXPENSES
Compensation and related expenses	326	338
Communications and technology	39	30
Occupancy and equipment costs	0	0
Clearing and exchange fees	0	0
Interest	3,375	3,281
Other	387	327
Total expenses	4,127	3,976
Income (Loss) before income taxes from continuing operations	(4,127)	(3,976)
Income Tax Expense (Benefit)	(1,040)	(1,528)
Net income (loss) from continuing operations	(3,087)	(2,448)
Income from discontinued operations		0
Equity in earnings of subsidiaries	9,792	(2,399)
Net income (loss)	6,705	(4,847)
Income taxes		0
Net income from discontinued operations		0
Less net income attributable to non-controlling interest, net of tax	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	6,705	(4,847)
Other comprehensive loss	0	0
Total comprehensive income	$ 6,705	$ (4,847)