Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES
Commissions									$ 329,668	$ 336,620	$ 377,317
Investment Advisory Fee Revenue									314,349	320,746	269,119
Investment banking									115,353	78,215	81,011
Sweep Interest Income from FDIC-Insured Bank Deposits									116,052	76,839	36,316
Interest									52,484	48,498	47,649
Principal transactions, net									14,461	23,273	20,481
Other									15,787	36,147	25,886
Total revenue	$ 243,254	$ 237,814	$ 242,556	$ 234,530	$ 264,973	$ 226,220	$ 215,884	$ 213,261	958,154	920,338	857,779
EXPENSES
Compensation and related expenses									607,192	602,138	584,710
Communications and technology									74,479	71,978	70,390
Occupancy and equipment costs									61,171	61,164	60,791
Clearing and exchange fees									22,985	23,545	25,126
Interest									46,396	28,354	19,437
Other									101,078	113,423	119,217
Total expenses	227,671	230,670	230,055	224,905	248,403	214,392	217,521	220,286	913,301	900,602	879,671
Income (loss) before income taxes from continuing operations	15,583	7,144	12,501	9,625	16,570	11,828	(1,637)	(7,025)	44,853	19,736	(21,892)
Other Income Tax Expense (Benefit), Continuing Operations	7,316	2,083	3,662	2,916	(4,598)	4,425	(274)	(1,687)	15,977	(2,134)	(12,262)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	8,267	5,061	8,839	6,709	21,168	7,403	(1,363)	(5,338)	28,876	21,870	(9,630)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax									0	2,071	17,339
Equity in earnings of subsidiaries									0	0	0
Net income	8,267	5,061	8,839	6,709	21,197	7,864	(1,310)	(4,751)	28,876	23,000	491
Discontinued Operation, Tax Effect of Discontinued Operation									0	941	7,218
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	0	0	0	0	29	461	53	587	0	1,130	10,121
Less net income (loss) attributable to non-controlling interest, net of tax	6	(10)	(16)	4	4	75	9	96	(16)	184	1,652
Net income (loss) attributable to Oppenheimer Holdings Inc.	$ 8,261	$ 5,071	$ 8,855	$ 6,705	$ 21,193	$ 7,789	$ (1,319)	$ (4,847)	28,892	22,816	(1,161)
Other comprehensive income									(1,417)	2,263	220
Total comprehensive income									27,475	25,079	(941)
Eliminations
REVENUES
Commissions									0	0	0
Investment Advisory Fee Revenue									(4,418)	(4,120)	(4,215)
Investment banking									0	(3,000)	0
Sweep Interest Income from FDIC-Insured Bank Deposits									0	0	0
Interest									(8,310)	(9,639)	(10,397)
Principal transactions, net									(54)	0	0
Other									(438)	(359)	(325)
Total revenue									(13,220)	(17,118)	(14,937)
EXPENSES
Compensation and related expenses									0	0	0
Communications and technology									0	0	0
Occupancy and equipment costs									(439)	(359)	(325)
Clearing and exchange fees									0	0	0
Interest									(8,309)	(9,639)	(10,397)
Other									(4,418)	(7,120)	(4,215)
Total expenses									(13,166)	(17,118)	(14,937)
Income (loss) before income taxes from continuing operations									0	0	0
Other Income Tax Expense (Benefit), Continuing Operations									0	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									0	0	0
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax										0	0
Equity in earnings of subsidiaries									(77,285)	(48,588)	(6,294)
Net income									(77,285)	(48,588)	(6,294)
Discontinued Operation, Tax Effect of Discontinued Operation										0	0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										0	0
Less net income (loss) attributable to non-controlling interest, net of tax									0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.									(77,285)	(48,588)	(6,294)
Other comprehensive income									0	0	0
Total comprehensive income									(77,285)	(48,588)	(6,294)
Guarantor Subsidiaries
REVENUES
Commissions									0	0	0
Investment Advisory Fee Revenue									1,938	1,752	1,571
Investment banking									0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits									0	0	0
Interest									8,247	9,589	10,242
Principal transactions, net									0	17	16
Other									443	361	326
Total revenue									10,628	11,719	12,155
EXPENSES
Compensation and related expenses									0	0	0
Communications and technology									0	0	0
Occupancy and equipment costs									0	0	0
Clearing and exchange fees									0	0	0
Interest									0	0	0
Other									4,059	1,382	1,284
Total expenses									4,059	1,382	1,284
Income (loss) before income taxes from continuing operations									6,569	10,337	10,871
Other Income Tax Expense (Benefit), Continuing Operations									2,052	(12,655)	3,325
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									4,517	22,992	7,546
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax										0	0
Equity in earnings of subsidiaries									36,411	12,798	(626)
Net income									40,928	35,790	6,920
Discontinued Operation, Tax Effect of Discontinued Operation										0	0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										0	0
Less net income (loss) attributable to non-controlling interest, net of tax									0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.									40,928	35,790	6,920
Other comprehensive income									0	0	0
Total comprehensive income									40,928	35,790	6,920
Non-Guarantor Subsidiaries
REVENUES
Commissions									329,668	336,620	377,317
Investment Advisory Fee Revenue									316,829	323,114	271,763
Investment banking									115,353	81,215	81,011
Sweep Interest Income from FDIC-Insured Bank Deposits									116,052	76,839	36,316
Interest									52,481	48,548	47,804
Principal transactions, net									14,515	23,256	20,465
Other									15,782	36,123	25,885
Total revenue									960,680	925,715	860,561
EXPENSES
Compensation and related expenses									605,644	600,901	583,469
Communications and technology									74,316	71,818	70,266
Occupancy and equipment costs									61,610	61,523	61,116
Clearing and exchange fees									22,985	23,545	25,126
Interest									41,205	24,253	16,709
Other									100,229	114,192	120,261
Total expenses									905,989	896,232	876,947
Income (loss) before income taxes from continuing operations									54,691	29,483	(16,386)
Other Income Tax Expense (Benefit), Continuing Operations									18,296	17,631	(7,291)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									36,395	11,852	(9,095)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax										2,071	17,339
Equity in earnings of subsidiaries									0	0	0
Net income									36,395	12,982	1,026
Discontinued Operation, Tax Effect of Discontinued Operation										941	7,218
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										1,130	10,121
Less net income (loss) attributable to non-controlling interest, net of tax									(16)	184	1,652
Net income (loss) attributable to Oppenheimer Holdings Inc.									36,411	12,798	(626)
Other comprehensive income									(1,417)	2,263	220
Total comprehensive income									34,994	15,061	(406)
Parent
REVENUES
Commissions									0	0	0
Investment Advisory Fee Revenue									0	0	0
Investment banking									0	0	0
Sweep Interest Income from FDIC-Insured Bank Deposits									0	0	0
Interest									66	0	0
Principal transactions, net									0	0	0
Other									0	22	0
Total revenue									66	22	0
EXPENSES
Compensation and related expenses									1,548	1,237	1,241
Communications and technology									163	160	124
Occupancy and equipment costs									0	0	0
Clearing and exchange fees									0	0	0
Interest									13,500	13,740	13,125
Other									1,208	4,969	1,887
Total expenses									16,419	20,106	16,377
Income (loss) before income taxes from continuing operations									(16,353)	(20,084)	(16,377)
Other Income Tax Expense (Benefit), Continuing Operations									(4,371)	(7,110)	(8,296)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest									(11,982)	(12,974)	(8,081)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax										0	0
Equity in earnings of subsidiaries									40,874	35,790	6,920
Net income									28,892	22,816	(1,161)
Discontinued Operation, Tax Effect of Discontinued Operation										0	0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										0	0
Less net income (loss) attributable to non-controlling interest, net of tax									0	0	0
Net income (loss) attributable to Oppenheimer Holdings Inc.									28,892	22,816	(1,161)
Other comprehensive income									0	0	0
Total comprehensive income									$ 28,892	$ 22,816	$ (1,161)