Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
REVENUES
Commissions	$ 103,249	$ 79,409
Investment Advisory Fee Revenue	86,164	73,647
Investment banking	25,728	28,043
Sweep Interest Income from FDIC-Insured Bank Deposits	18,826	33,968
Interest	10,890	12,727
Principal transactions, net	(868)	11,438
Other	(9,219)	12,538
Total revenue	234,770	251,770
EXPENSES
Compensation and related expenses	157,676	160,355
Communications and technology	19,891	20,086
Occupancy and equipment costs	16,078	15,273
Clearing and exchange fees	5,659	5,332
Interest	6,550	12,986
Other	18,693	21,686
Total expenses	224,547	235,718
Operating Income (Loss)	10,223	16,052
Income Tax Expense (Benefit)	2,405	4,858
Net Income (Loss) before equity in Earnings of Subsidiaries	7,818	11,194
Equity in earnings of subsidiaries	0	0
Net income attributable to Oppenheimer Holdings Inc.	7,818	11,194
Other comprehensive income	(537)	563
Comprehensive income	7,281	11,757
Eliminations
REVENUES
Commissions	0	0
Investment Advisory Fee Revenue	(354)	(335)
Investment banking	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0
Interest	(2,067)	0
Principal transactions, net	0	(2,073)
Other	(4)	0
Total revenue	(2,425)	(2,408)
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	(2,068)	(2,074)
Other	(357)	(334)
Total expenses	(2,425)	(2,408)
Operating Income (Loss)	0	0
Income Tax Expense (Benefit)	0	0
Net Income (Loss) before equity in Earnings of Subsidiaries	0	0
Equity in earnings of subsidiaries	(18,725)	(26,825)
Net income attributable to Oppenheimer Holdings Inc.	(18,725)	(26,825)
Other comprehensive income	0	0
Comprehensive income	(18,725)	(26,825)
Parent
REVENUES
Commissions	0	0
Investment Advisory Fee Revenue	0	0
Investment banking	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0
Interest	1	0
Principal transactions, net	0	84
Other	86	0
Total revenue	87	84
EXPENSES
Compensation and related expenses	314	445
Communications and technology	40	39
Occupancy and equipment costs	0	0
Clearing and exchange fees	0	0
Interest	2,530	3,375
Other	233	316
Total expenses	3,117	4,175
Operating Income (Loss)	(3,030)	(4,091)
Income Tax Expense (Benefit)	(740)	(1,343)
Net Income (Loss) before equity in Earnings of Subsidiaries	(2,290)	(2,748)
Equity in earnings of subsidiaries	10,108	13,942
Net income attributable to Oppenheimer Holdings Inc.	7,818	11,194
Other comprehensive income	0	0
Comprehensive income	7,818	11,194
Guarantor Subsidiaries
REVENUES
Commissions	0	0
Investment Advisory Fee Revenue	0	0
Investment banking	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits	0	49
Interest	2,058	0
Principal transactions, net	(16)	2,062
Other	0	1
Total revenue	2,042	2,112
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	2	122
Total expenses	2	122
Operating Income (Loss)	2,040	1,990
Income Tax Expense (Benefit)	549	926
Net Income (Loss) before equity in Earnings of Subsidiaries	1,491	1,064
Equity in earnings of subsidiaries	8,617	12,883
Net income attributable to Oppenheimer Holdings Inc.	10,108	13,947
Other comprehensive income	0	0
Comprehensive income	10,108	13,947
Non-Guarantor Subsidiaries
REVENUES
Commissions	103,249	79,409
Investment Advisory Fee Revenue	86,518	73,982
Investment banking	25,728	28,043
Sweep Interest Income from FDIC-Insured Bank Deposits	18,826	11,389
Interest	10,898	33,968
Principal transactions, net	(852)	12,654
Other	(9,301)	12,537
Total revenue	235,066	251,982
EXPENSES
Compensation and related expenses	157,362	159,910
Communications and technology	19,851	20,047
Occupancy and equipment costs	16,078	15,273
Clearing and exchange fees	5,659	5,332
Interest	6,088	11,685
Other	18,815	21,582
Total expenses	223,853	233,829
Operating Income (Loss)	11,213	18,153
Income Tax Expense (Benefit)	2,596	5,275
Net Income (Loss) before equity in Earnings of Subsidiaries	8,617	12,878
Equity in earnings of subsidiaries	0	0
Net income attributable to Oppenheimer Holdings Inc.	8,617	12,878
Other comprehensive income	(537)	563
Comprehensive income	$ 8,080	$ 13,441