Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
REVENUES
Commissions	$ 80,896	$ 82,850	$ 160,305	$ 166,257
Investment Advisory Fee Revenue	80,707	77,270	154,354	154,818
Investment banking	32,006	27,904	60,049	56,114
Sweep Interest Income from FDIC-Insured Bank Deposits	31,830	28,853	65,798	54,150
Interest	13,550	13,056	26,277	25,283
Principal transactions, net	3,045	6,400	14,483	9,126
Other	8,901	6,223	21,439	11,338
Total revenue	250,935	242,556	502,705	477,086
EXPENSES
Compensation and related expenses	155,783	151,871	316,138	304,975
Communications and technology	20,499	17,997	40,585	36,685
Occupancy and equipment costs	15,573	14,901	30,846	30,329
Clearing and exchange fees	5,678	5,780	11,010	11,876
Interest	13,192	10,909	26,178	19,872
Other	22,819	28,581	44,505	51,211
Total expenses	233,544	230,039	469,262	454,948
Operating Income (Loss)	17,391	12,517	33,443	22,138
Income Tax Expense (Benefit)	5,016	3,662	9,874	6,578
Net Income (Loss) before equity in Earnings of Subsidiaries	12,375	8,855	23,569	15,560
Equity in earnings of subsidiaries	0	0	0	0
Net income attributable to Oppenheimer Holdings Inc.	12,375	8,855	23,569	15,560
Other comprehensive income	361	(837)	924	(979)
Comprehensive income	12,736	8,018	24,493	14,581
Eliminations
REVENUES
Commissions	0	0	0	0
Investment Advisory Fee Revenue	(360)	(319)	(695)	(645)
Investment banking	0	0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	(9)	0	0
Interest	(2,074)	0	(4,147)	(4,157)
Principal transactions, net	0	(2,077)	(12)	(42)
Other	1	(94)	1	(189)
Total revenue	(2,433)	(2,499)	(4,853)	(5,033)
EXPENSES
Compensation and related expenses	1	0	(5)	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	0	(94)	0	(189)
Clearing and exchange fees	0	0	0	0
Interest	(2,073)	(2,077)	(4,147)	(4,157)
Other	(361)	(328)	(701)	(687)
Total expenses	(2,433)	(2,499)	(4,853)	(5,033)
Operating Income (Loss)	0	0	0	0
Income Tax Expense (Benefit)	0	0	0	0
Net Income (Loss) before equity in Earnings of Subsidiaries	0	0	0	0
Equity in earnings of subsidiaries	(29,191)	(23,085)	(55,998)	(41,030)
Net income attributable to Oppenheimer Holdings Inc.	(29,191)	(23,085)	(55,998)	(41,030)
Other comprehensive income	0	0	0	0
Comprehensive income	(29,191)	(23,085)	(55,998)	(41,030)
Guarantor Subsidiaries
REVENUES
Commissions	0	0	0	0
Investment Advisory Fee Revenue	0	0	0	0
Investment banking	0	0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0	0	0
Interest	2,060	0	4,122	4,120
Principal transactions, net	40	2,060	101	0
Other	1	95	2	191
Total revenue	2,101	2,155	4,225	4,311
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	122	849	244	1,102
Total expenses	122	849	244	1,102
Operating Income (Loss)	1,979	1,306	3,981	3,209
Income Tax Expense (Benefit)	510	369	1,436	633
Net Income (Loss) before equity in Earnings of Subsidiaries	1,469	937	2,545	2,576
Equity in earnings of subsidiaries	13,861	11,074	26,726	19,227
Net income attributable to Oppenheimer Holdings Inc.	15,330	12,011	29,271	21,803
Other comprehensive income	0	0	0	0
Comprehensive income	15,330	12,011	29,271	21,803
Non-Guarantor Subsidiaries
REVENUES
Commissions	80,896	82,850	160,305	166,257
Investment Advisory Fee Revenue	81,067	77,589	155,049	155,463
Investment banking	32,006	27,904	60,049	56,114
Sweep Interest Income from FDIC-Insured Bank Deposits	31,830	6,409	65,798	54,150
Interest	13,473	28,853	26,127	25,317
Principal transactions, net	3,005	13,070	14,394	9,168
Other	8,899	6,222	21,436	11,336
Total revenue	251,176	242,897	503,158	477,805
EXPENSES
Compensation and related expenses	155,402	151,349	315,318	304,127
Communications and technology	20,447	17,948	40,494	36,597
Occupancy and equipment costs	15,573	14,995	30,846	30,518
Clearing and exchange fees	5,678	5,780	11,010	11,876
Interest	11,890	9,611	23,575	17,279
Other	22,824	27,782	44,412	50,131
Total expenses	231,814	227,465	465,655	450,528
Operating Income (Loss)	19,362	15,432	37,503	27,277
Income Tax Expense (Benefit)	5,501	4,358	10,776	8,050
Net Income (Loss) before equity in Earnings of Subsidiaries	13,861	11,074	26,727	19,227
Equity in earnings of subsidiaries	0	0	0	0
Net income attributable to Oppenheimer Holdings Inc.	13,861	11,074	26,727	19,227
Other comprehensive income	361	(837)	924	(979)
Comprehensive income	14,222	10,237	27,651	18,248
Parent
REVENUES
Commissions	0	0	0	0
Investment Advisory Fee Revenue	0	0	0	0
Investment banking	0	0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0	0	0
Interest	91	0	175	3
Principal transactions, net	0	3	0	0
Other	0	0	0	0
Total revenue	91	3	175	3
EXPENSES
Compensation and related expenses	380	522	825	848
Communications and technology	52	49	91	88
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	3,375	3,375	6,750	6,750
Other	234	278	550	665
Total expenses	4,041	4,224	8,216	8,351
Operating Income (Loss)	(3,950)	(4,221)	(8,041)	(8,348)
Income Tax Expense (Benefit)	(995)	(1,065)	(2,338)	(2,105)
Net Income (Loss) before equity in Earnings of Subsidiaries	(2,955)	(3,156)	(5,703)	(6,243)
Equity in earnings of subsidiaries	15,330	12,011	29,272	21,803
Net income attributable to Oppenheimer Holdings Inc.	12,375	8,855	23,569	15,560
Other comprehensive income	0	0	0	0
Comprehensive income	$ 12,375	$ 8,855	$ 23,569	$ 15,560