Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
REVENUES
Commissions	$ 78,627	$ 79,678	$ 238,932	$ 245,935
Investment Advisory Fee Revenue	80,887	78,154	235,241	232,972
Investment banking	21,798	28,328	81,847	84,442
Sweep Interest Income from FDIC-Insured Bank Deposits	28,894	30,053	94,692	84,203
Interest	12,344	13,403	38,621	38,686
Principal transactions, net	7,606	(16)	22,089	9,110
Other	4,637	8,214	26,076	19,552
Total revenue	234,793	237,814	737,498	714,900
EXPENSES
Compensation and related expenses	151,284	152,846	467,422	457,821
Communications and technology	20,872	18,602	61,457	55,287
Occupancy and equipment costs	16,010	15,106	46,856	45,435
Clearing and exchange fees	5,469	5,378	16,479	17,254
Interest	11,531	12,915	37,709	32,787
Other	23,131	25,813	67,636	77,024
Total expenses	228,297	230,660	697,559	685,608
Operating Income (Loss)	6,496	7,154	39,939	29,292
Income Tax Expense (Benefit)	2,547	2,083	12,421	8,661
Net Income (Loss) before equity in Earnings of Subsidiaries	3,949	5,071	27,518	20,631
Equity in earnings of subsidiaries	0	0	0	0
Net income attributable to Oppenheimer Holdings Inc.	3,949	5,071	27,518	20,631
Other comprehensive income	533	99	1,457	(880)
Comprehensive income	4,482	5,170	28,975	19,751
Eliminations
REVENUES
Commissions	0	0	0	0
Investment Advisory Fee Revenue	(342)	(336)	(1,037)	(981)
Investment banking	0	0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	3	0	0
Interest	(2,073)	0	(6,220)	(6,233)
Principal transactions, net	54	(2,076)	(12)	(39)
Other	(1)	(153)	1	(342)
Total revenue	(2,362)	(2,562)	(7,268)	(7,595)
EXPENSES
Compensation and related expenses	(1)	0	(6)	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	0	(153)	2	(342)
Clearing and exchange fees	54	0	0	0
Interest	(2,073)	(2,076)	(6,220)	(6,233)
Other	(342)	(333)	(1,044)	(1,020)
Total expenses	(2,362)	(2,562)	(7,268)	(7,595)
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	(14,403)	(14,662)	(70,401)	(55,692)
Net income attributable to Oppenheimer Holdings Inc.	(14,403)	(14,662)	(70,401)	(55,692)
Other comprehensive income	0	0	0	0
Comprehensive income	(14,403)	(14,662)	(70,401)	(55,692)
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	59	0	234	4
Principal transactions, net	0	1	0	0
Other	3	0	3	0
Total revenue	62	1	237	4
EXPENSES
Compensation and related expenses	273	343	1,098	1,191
Communications and technology	39	35	130	123
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	3,038	3,375	9,788	10,125
Other	2,087	218	2,637	883
Total expenses	5,437	3,971	13,653	12,322
Operating Income (Loss)	(5,375)	(3,970)	(13,416)	(12,318)
Income Tax Expense (Benefit)	(1,364)	(976)	(3,702)	(3,081)
Net Income (Loss) before equity in Earnings of Subsidiaries	(4,011)	(2,994)	(9,714)	(9,237)
Equity in earnings of subsidiaries	7,960	8,065	37,232	29,868
Net income attributable to Oppenheimer Holdings Inc.	3,949	5,071	27,518	20,631
Other comprehensive income	0	0	0	0
Comprehensive income	3,949	5,071	27,518	20,631
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	2,059	0	6,181	6,183
Principal transactions, net	(34)	2,063	121	0
Other	0	154	2	345
Total revenue	2,025	2,217	6,304	6,528
EXPENSES
Compensation and related expenses	0	0	0	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	0	0	(1)	0
Clearing and exchange fees	(54)	0	0	0
Interest	0	0	0	0
Other	4	270	248	1,372
Total expenses	(50)	270	247	1,372
Operating Income (Loss)	2,075	1,947	6,057	5,156
Income Tax Expense (Benefit)	558	479	1,994	1,112
Net Income (Loss) before equity in Earnings of Subsidiaries	1,517	1,468	4,063	4,044
Equity in earnings of subsidiaries	6,443	6,597	33,169	25,824
Net income attributable to Oppenheimer Holdings Inc.	7,960	8,065	37,232	29,868
Other comprehensive income	0	0	0	0
Comprehensive income	7,960	8,065	37,232	29,868
Non-Guarantor Subsidiaries
REVENUES
Commissions	78,627	79,678	238,932	245,935
Investment Advisory Fee Revenue	81,229	78,490	236,278	233,953
Investment banking	21,798	28,328	81,847	84,442
Sweep Interest Income from FDIC-Insured Bank Deposits	28,894	(19)	94,692	84,203
Interest	12,299	30,053	38,426	38,732
Principal transactions, net	7,586	13,415	21,980	9,149
Other	4,635	8,213	26,070	19,549
Total revenue	235,068	238,158	738,225	715,963
EXPENSES
Compensation and related expenses	151,012	152,503	466,330	456,630
Communications and technology	20,833	18,567	61,327	55,164
Occupancy and equipment costs	16,010	15,259	46,855	45,777
Clearing and exchange fees	5,469	5,378	16,479	17,254
Interest	10,566	11,616	34,141	28,895
Other	21,382	25,658	65,795	75,789
Total expenses	225,272	228,981	690,927	679,509
Operating Income (Loss)	9,796	9,177	47,298	36,454
Income Tax Expense (Benefit)	3,353	2,580	14,129	10,630
Net Income (Loss) before equity in Earnings of Subsidiaries	6,443	6,597	33,169	25,824
Equity in earnings of subsidiaries	0	0	0	0
Net income attributable to Oppenheimer Holdings Inc.	6,443	6,597	33,169	25,824
Other comprehensive income	533	99	1,457	(880)
Comprehensive income	$ 6,976	$ 6,696	$ 34,626	$ 24,944