Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
REVENUES
Commissions	$ 82,850	$ 83,852	$ 166,257	$ 170,569
Advisory fees	77,270	72,783	154,818	142,192
Investment banking	27,904	15,386	56,114	33,407
Sweep Interest Income from FDIC-Insured Bank Deposits	28,853	17,720	54,150	31,846
Interest	13,056	12,829	25,283	23,394
Principal transactions, net	6,400	5,302	9,126	10,675
Other	6,223	8,012	11,338	17,062
Total revenue	242,556	215,884	477,086	429,145
EXPENSES
Compensation and related expenses	151,871	142,657	304,975	286,535
Communications and technology	17,997	18,399	36,685	36,105
Occupancy and equipment costs	14,901	15,161	30,329	30,433
Clearing and exchange fees	5,780	5,916	11,876	11,770
Interest	10,909	6,854	19,872	12,210
Other	28,597	28,534	51,223	60,754
Total expenses	230,055	217,521	454,960	437,807
Income (Loss) before income taxes from continuing operations	12,501	(1,637)	22,126	(8,662)
Income Tax Expense (Benefit)	3,662	(274)	6,578	(1,961)
Net income (loss) from continuing operations	8,839	(1,363)	15,548	(6,701)
Income from discontinued operations	0	89	0	1,065
Equity in earnings of subsidiaries	0	0	0	0
Net income (loss)	8,839	(1,310)	15,548	(6,061)
Income taxes	0	36	0	425
Net income from discontinued operations	0	53	0	640
Less net income (loss) attributable to non-controlling interest, net of tax	(16)	9	(12)	105
Net income (loss) attributable to Oppenheimer Holdings Inc.	8,855	(1,319)	15,560	(6,166)
Other comprehensive loss	(837)	780	(979)	2,204
Total comprehensive income	8,018	(539)	14,581	(3,962)
Eliminations
REVENUES
Commissions	0	0	0	0
Advisory fees	(319)	(343)	(645)	(663)
Investment banking	0	(3,000)	0	(3,000)
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0	(4,157)	0
Interest	(2,077)	(2,575)	(42)	(5,151)
Principal transactions, net	(9)	0	0	0
Other	(94)	(89)	(189)	(177)
Total revenue	(2,499)	(6,007)	(5,033)	(8,991)
EXPENSES
Compensation and related expenses	0	0	0	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	(94)	(89)	(189)	(177)
Clearing and exchange fees	0	0	0	0
Interest	(2,077)	(2,575)	(4,157)	(5,151)
Other	(328)	(3,343)	(687)	(3,663)
Total expenses	(2,499)	(6,007)	(5,033)	(8,991)
Income (Loss) before income taxes from continuing operations	0	0	0	0
Income Tax Expense (Benefit)	0	0	0	0
Net income (loss) from continuing operations	0	0	0	0
Income from discontinued operations		0		0
Equity in earnings of subsidiaries	(23,085)	(5,753)	(41,030)	726
Net income (loss)	(23,085)	(5,753)	(41,030)	726
Income taxes		0		0
Net income from discontinued operations		0		0
Less net income (loss) attributable to non-controlling interest, net of tax	0	0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	(23,085)	(5,753)	(41,030)	726
Other comprehensive loss	0	0	0	0
Total comprehensive income	(23,085)	(5,753)	(41,030)	726
Guarantor Subsidiaries
REVENUES
Commissions	0	0	0	0
Advisory fees	0	0	0	0
Investment banking	0	0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0	4,120	0
Interest	2,060	2,559	0	5,138
Principal transactions, net	0	9	0	15
Other	95	90	191	178
Total revenue	2,155	2,658	4,311	5,331
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	849	195	1,102	267
Total expenses	849	195	1,102	267
Income (Loss) before income taxes from continuing operations	1,306	2,463	3,209	5,064
Income Tax Expense (Benefit)	369	956	633	1,876
Net income (loss) from continuing operations	937	1,507	2,576	3,188
Income from discontinued operations		0		0
Equity in earnings of subsidiaries	11,074	2,123	19,227	(1,957)
Net income (loss)	12,011	3,630	21,803	1,231
Income taxes		0		0
Net income from discontinued operations		0		0
Less net income (loss) attributable to non-controlling interest, net of tax	0	0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	12,011	3,630	21,803	1,231
Other comprehensive loss	0	0	0	0
Total comprehensive income	12,011	3,630	21,803	1,231
Non-Guarantor Subsidiaries
REVENUES
Commissions	82,850	83,852	166,257	170,569
Advisory fees	77,589	73,126	155,463	142,855
Investment banking	27,904	18,386	56,114	36,407
Sweep Interest Income from FDIC-Insured Bank Deposits	28,853	17,720	25,317	31,846
Interest	13,070	12,845	9,168	23,407
Principal transactions, net	6,409	5,293	54,150	10,660
Other	6,222	8,011	11,336	17,061
Total revenue	242,897	219,233	477,805	432,805
EXPENSES
Compensation and related expenses	151,349	142,290	304,127	285,830
Communications and technology	17,948	18,350	36,597	36,026
Occupancy and equipment costs	14,995	15,250	30,518	30,610
Clearing and exchange fees	5,780	5,916	11,876	11,770
Interest	9,611	5,720	17,279	10,371
Other	27,798	27,760	50,143	59,901
Total expenses	227,481	215,286	450,540	434,508
Income (Loss) before income taxes from continuing operations	15,416	3,947	27,265	(1,703)
Income Tax Expense (Benefit)	4,358	1,868	8,050	789
Net income (loss) from continuing operations	11,058	2,079	19,215	(2,492)
Income from discontinued operations		89		1,065
Equity in earnings of subsidiaries	0	0	0	0
Net income (loss)	11,058	2,132	19,215	(1,852)
Income taxes		36		425
Net income from discontinued operations		53		640
Less net income (loss) attributable to non-controlling interest, net of tax	(16)	9	(12)	105
Net income (loss) attributable to Oppenheimer Holdings Inc.	11,074	2,123	19,227	(1,957)
Other comprehensive loss	(837)	780	(979)	2,204
Total comprehensive income	10,237	2,903	18,248	247
Parent
REVENUES
Commissions	0	0	0	0
Advisory fees	0	0	0	0
Investment banking	0	0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0	3	0
Interest	3	0	0	0
Principal transactions, net	0	0	0	0
Other	0	0	0	0
Total revenue	3	0	3	0
EXPENSES
Compensation and related expenses	522	367	848	705
Communications and technology	49	49	88	79
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	3,375	3,709	6,750	6,990
Other	278	3,922	665	4,249
Total expenses	4,224	8,047	8,351	12,023
Income (Loss) before income taxes from continuing operations	(4,221)	(8,047)	(8,348)	(12,023)
Income Tax Expense (Benefit)	(1,065)	(3,098)	(2,105)	(4,626)
Net income (loss) from continuing operations	(3,156)	(4,949)	(6,243)	(7,397)
Income from discontinued operations		0		0
Equity in earnings of subsidiaries	12,011	3,630	21,803	1,231
Net income (loss)	8,855	(1,319)	15,560	(6,166)
Income taxes		0		0
Net income from discontinued operations		0		0
Less net income (loss) attributable to non-controlling interest, net of tax	0	0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.	8,855	(1,319)	15,560	(6,166)
Other comprehensive loss	0	0	0	0
Total comprehensive income	$ 8,855	$ (1,319)	$ 15,560	$ (6,166)