Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Income (Loss) before equity in Earnings of Subsidiaries	$ 15,639	$ 3,949	$ 41,106	$ 27,518
Other comprehensive income	244	533	187	1,457
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	15,883	4,482	41,293	28,975
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	0	0	0	0
REVENUE
Commissions	92,241	78,627	297,126	238,932
Investment Advisory Fee Revenue	88,595	80,887	250,740	235,241
Investment banking	66,245	21,798	138,159	81,847
Proceeds from (Payments for) in Interest-bearing Deposits in Banks	4,619	28,894	30,567	94,692
Interest	7,540	12,344	24,650	38,621
Principal transactions, net	7,703	7,606	18,899	22,089
Other	9,316	4,637	15,618	26,076
Total revenue	276,259	234,793	775,759	737,498
EXPENSES
Compensation and related expenses	189,654	151,284	526,924	467,422
Communications and technology	19,474	20,872	60,689	61,457
Occupancy and equipment costs	15,199	16,010	46,611	46,856
Clearing and exchange fees	6,211	5,469	18,061	16,479
Interest	3,461	11,531	12,901	37,709
Other	20,542	23,131	55,368	67,636
Total expenses	254,541	228,297	720,554	697,559
Operating Income (Loss)	21,718	6,496	55,205	39,939
Income Tax Expense (Benefit)	6,079	2,547	14,099	12,421
Net income attributable to Oppenheimer Holdings Inc.	$ 15,639	$ 3,949	$ 41,106	$ 27,518
Earnings per share
Net loss per share (in dollars per share)	$ 1.25	$ 0.31	$ 3.24	$ 2.13
Earnings Per Share, Diluted [Abstract]
Net loss per share (in dollars per share)	$ 1.19	$ 0.29	$ 3.12	$ 1.99
Weighted average shares
Basic (in shares)	12,553,802	12,825,944	12,696,143	12,940,129
Diluted (in shares)	13,146,586	13,832,994	13,194,434	13,846,139
Parent [Member]
Net Income (Loss) before equity in Earnings of Subsidiaries	$ (5,812)	$ (4,011)	$ (10,340)	$ (9,714)
Other comprehensive income	0	0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	15,639	3,949	41,106	27,518
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	21,451	7,960	51,446	37,232
REVENUE
Commissions	0	0	0	0
Investment Advisory Fee Revenue	0	0	0	0
Investment banking	0	0	0	0
Proceeds from (Payments for) in Interest-bearing Deposits in Banks	0	0	0	0
Interest	0	59	2	234
Principal transactions, net	0	0	0	0
Other	0	3	95	3
Total revenue	0	62	97	237
EXPENSES
Compensation and related expenses	259	273	879	1,098
Communications and technology	61	39	144	130
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	2,596	3,038	7,632	9,788
Other	4,906	2,087	5,358	2,637
Total expenses	7,822	5,437	14,013	13,653
Operating Income (Loss)	(7,822)	(5,375)	(13,916)	(13,416)
Income Tax Expense (Benefit)	(2,010)	(1,364)	(3,576)	(3,702)
Net income attributable to Oppenheimer Holdings Inc.	15,639	3,949	41,106	27,518
Guarantor Subsidiaries [Member]
Net Income (Loss) before equity in Earnings of Subsidiaries	1,535	1,517	4,600	4,063
Other comprehensive income	0	0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	21,451	7,960	51,446	37,232
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	19,916	6,443	46,846	33,169
REVENUE
Commissions	0	0	0	0
Investment Advisory Fee Revenue	0	0	0	0
Investment banking	0	0	0	0
Proceeds from (Payments for) in Interest-bearing Deposits in Banks	0	0	0	0
Interest	2,058	2,059	6,174	6,181
Principal transactions, net	8	(34)	57	121
Other	0	0	0	2
Total revenue	2,066	2,025	6,231	6,304
EXPENSES
Compensation and related expenses	0	0	0	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	0	0	0	(1)
Clearing and exchange fees	0	(54)	0	0
Interest	0	0	0	0
Other	3	4	8	248
Total expenses	3	(50)	8	247
Operating Income (Loss)	2,063	2,075	6,223	6,057
Income Tax Expense (Benefit)	528	558	1,623	1,994
Net income attributable to Oppenheimer Holdings Inc.	21,451	7,960	51,446	37,232
Non-Guarantor Subsidiaries [Member]
Net Income (Loss) before equity in Earnings of Subsidiaries	19,916	6,443	46,846	33,169
Other comprehensive income	244	533	187	1,457
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	20,160	6,976	47,033	34,626
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	0	0	0	0
REVENUE
Commissions	92,241	78,627	297,126	238,932
Investment Advisory Fee Revenue	88,963	81,229	251,811	236,278
Investment banking	68,120	21,798	140,034	81,847
Proceeds from (Payments for) in Interest-bearing Deposits in Banks	4,619	28,894	30,567	94,692
Interest	7,594	12,299	24,732	38,426
Principal transactions, net	7,695	7,586	18,842	21,980
Other	9,315	4,635	15,526	26,070
Total revenue	278,547	235,068	778,638	738,225
EXPENSES
Compensation and related expenses	189,395	151,012	526,045	466,330
Communications and technology	19,413	20,833	60,545	61,327
Occupancy and equipment costs	15,199	16,010	46,611	46,855
Clearing and exchange fees	6,211	5,469	18,061	16,479
Interest	2,977	10,566	11,527	34,141
Other	17,875	21,382	52,951	65,795
Total expenses	251,070	225,272	715,740	690,927
Operating Income (Loss)	27,477	9,796	62,898	47,298
Income Tax Expense (Benefit)	7,561	3,353	16,052	14,129
Net income attributable to Oppenheimer Holdings Inc.	19,916	6,443	46,846	33,169
Consolidation, Eliminations [Member]
Net Income (Loss) before equity in Earnings of Subsidiaries				0
Other comprehensive income				0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent				(70,401)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(70,401)
EXPENSES
Total expenses				(7,268)
Operating Income (Loss)				0
Income Tax Expense (Benefit)				0
Net income attributable to Oppenheimer Holdings Inc.				(70,401)
Consolidation, Eliminations [Member]
Net Income (Loss) before equity in Earnings of Subsidiaries	0	0	0
Other comprehensive income	0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	(41,367)	(14,403)	(98,292)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(41,367)	(14,403)	(98,292)
REVENUE
Commissions	0	0	0	0
Investment Advisory Fee Revenue	(368)	(342)	(1,071)	(1,037)
Investment banking	(1,875)	0	(1,875)	0
Proceeds from (Payments for) in Interest-bearing Deposits in Banks	0	0	0	0
Interest	(2,112)	(2,073)	(6,258)	(6,220)
Principal transactions, net	0	54	0	(12)
Other	1	(1)	(3)	1
Total revenue	(4,354)	(2,362)	(9,207)	(7,268)
EXPENSES
Compensation and related expenses	0	(1)	0	(6)
Communications and technology	0	0	0	0
Occupancy and equipment costs	0	0	0	2
Clearing and exchange fees	0	54	0	0
Interest	(2,112)	(2,073)	(6,258)	(6,220)
Other	(2,242)	(342)	(2,949)	$ (1,044)
Total expenses	(4,354)	(2,362)	(9,207)
Operating Income (Loss)	0	0	0
Income Tax Expense (Benefit)	0	0	0
Net income attributable to Oppenheimer Holdings Inc.	$ (41,367)	$ (14,403)	$ (98,292)