Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
REVENUES
Commissions	$ 79,678	$ 77,635	$ 245,935	$ 248,204
Investment Advisory Fee Revenue	78,154	74,329	232,972	216,521
Investment banking	28,328	23,940	84,442	57,347
Sweep Interest Income from FDIC-Insured Bank Deposits	30,053	21,146	84,203	52,992
Interest	13,403	12,952	38,686	36,346
Principal transactions, net	(16)	5,135	9,110	15,810
Other	8,214	11,083	19,552	28,145
Total revenue	237,814	226,220	714,900	655,365
EXPENSES
Compensation and related expenses	152,846	142,090	457,821	428,625
Communications and technology	18,602	17,781	55,287	53,886
Occupancy and equipment costs	15,106	15,288	45,435	45,721
Clearing and exchange fees	5,378	5,622	17,254	17,392
Interest	12,915	6,500	32,787	18,710
Other	25,823	27,111	77,046	87,865
Total expenses	230,670	214,392	685,630	652,199
Income before income taxes from continuing operations	7,144	11,828	29,270	3,166
Income Tax Expense (Benefit)	2,083	4,425	8,661	2,464
Net income from continuing operations	5,061	7,403	20,609	702
Income from discontinued operations	0	769	0	1,834
Equity in earnings of subsidiaries	0	0	0	0
Net income	5,061	7,864	20,609	1,803
Income taxes	0	308	0	733
Net income from discontinued operations	0	461	0	1,101
Less net income (loss) attributable to non-controlling interest, net of tax	(10)	75	(22)	180
Net income attributable to Oppenheimer Holdings Inc.	5,071	7,789	20,631	1,623
Other comprehensive income	99	(251)	(880)	1,953
Total comprehensive income	5,170	7,538	19,751	3,576
Eliminations
REVENUES
Commissions	0	0	0	0
Investment Advisory Fee Revenue	(336)	(326)	(981)	(989)
Investment banking	0	0	0	(3,000)
Sweep Interest Income from FDIC-Insured Bank Deposits	0	0	(6,233)	0
Interest	(2,076)	(2,411)	(39)	(7,562)
Principal transactions, net	3	0	0	0
Other	(153)	(89)	(342)	(266)
Total revenue	(2,562)	(2,826)	(7,595)	(11,817)
EXPENSES
Compensation and related expenses	0	0	0	0
Communications and technology	0	0	0	0
Occupancy and equipment costs	(153)	(89)	(342)	(266)
Clearing and exchange fees	0	0		0
Interest	(2,076)	(2,411)	(6,233)	(7,562)
Other	(333)	(326)	(1,020)	(3,989)
Total expenses	(2,562)	(2,826)	(7,595)	(11,817)
Income before income taxes from continuing operations	0	0	0	0
Income Tax Expense (Benefit)	0	0	0	0
Net income from continuing operations	0	0	0	0
Income from discontinued operations		0		0
Equity in earnings of subsidiaries	(14,662)	(19,164)	(55,692)	(18,438)
Net income	(14,662)	(19,164)	(55,692)	(18,438)
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 attributable to Oppenheimer Holdings Inc.	(14,662)	(19,164)	(55,692)	(18,438)
Other comprehensive income	0	0	0	0
Total comprehensive income	(14,662)	(19,164)	(55,692)	(18,438)
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	6,183	0
Interest	2,063	2,391	0	7,529
Principal transactions, net	0	2	0	17
Other	154	89	345	267
Total revenue	2,217	2,482	6,528	7,813
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	270	62	1,372	329
Total expenses	270	62	1,372	329
Income before income taxes from continuing operations	1,947	2,420	5,156	7,484
Income Tax Expense (Benefit)	479	984	1,112	2,860
Net income from continuing operations	1,468	1,436	4,044	4,624
Income from discontinued operations		0		0
Equity in earnings of subsidiaries	6,597	8,864	25,824	6,907
Net income	8,065	10,300	29,868	11,531
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 attributable to Oppenheimer Holdings Inc.	8,065	10,300	29,868	11,531
Other comprehensive income	0	0	0	0
Total comprehensive income	8,065	10,300	29,868	11,531
Non-Guarantor Subsidiaries
REVENUES
Commissions	79,678	77,635	245,935	248,204
Investment Advisory Fee Revenue	78,490	74,655	233,953	217,510
Investment banking	28,328	23,940	84,442	60,347
Sweep Interest Income from FDIC-Insured Bank Deposits	30,053	21,146	38,732	52,992
Interest	13,415	12,972	9,149	36,379
Principal transactions, net	(19)	5,133	84,203	15,793
Other	8,213	11,061	19,549	28,122
Total revenue	238,158	226,542	715,963	659,347
EXPENSES
Compensation and related expenses	152,503	141,819	456,630	427,649
Communications and technology	18,567	17,748	55,164	53,774
Occupancy and equipment costs	15,259	15,377	45,777	45,987
Clearing and exchange fees	5,378	5,622	17,254	17,392
Interest	11,616	5,536	28,895	15,907
Other	25,668	26,963	75,811	86,864
Total expenses	228,991	213,065	679,531	647,573
Income before income taxes from continuing operations	9,167	13,477	36,432	11,774
Income Tax Expense (Benefit)	2,580	4,999	10,630	5,788
Net income from continuing operations	6,587	8,478	25,802	5,986
Income from discontinued operations		769		1,834
Equity in earnings of subsidiaries	0	0	0	0
Net income	6,587	8,939	25,802	7,087
Income taxes		308		733
Net income from discontinued operations		461		1,101
Less net income (loss) attributable to non-controlling interest, net of tax	(10)	75	(22)	180
Net income attributable to Oppenheimer Holdings Inc.	6,597	8,864	25,824	6,907
Other comprehensive income	99	(251)	(880)	1,953
Total comprehensive income	6,696	8,613	24,944	8,860
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	4	0
Interest	1	0	0	0
Principal transactions, net	0	0	0	0
Other	0	22	0	22
Total revenue	1	22	4	22
EXPENSES
Compensation and related expenses	343	271	1,191	976
Communications and technology	35	33	123	112
Occupancy and equipment costs	0	0	0	0
Clearing and exchange fees	0	0	0	0
Interest	3,375	3,375	10,125	10,365
Other	218	412	883	4,661
Total expenses	3,971	4,091	12,322	16,114
Income before income taxes from continuing operations	(3,970)	(4,069)	(12,318)	(16,092)
Income Tax Expense (Benefit)	(976)	(1,558)	(3,081)	(6,184)
Net income from continuing operations	(2,994)	(2,511)	(9,237)	(9,908)
Income from discontinued operations		0		0
Equity in earnings of subsidiaries	8,065	10,300	29,868	11,531
Net income	5,071	7,789	20,631	1,623
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 attributable to Oppenheimer Holdings Inc.	5,071	7,789	20,631	1,623
Other comprehensive income	0	0	0	0
Total comprehensive income	$ 5,071	$ 7,789	$ 20,631	$ 1,623