Supplemental Guarantor Condensed Consolidated Financial Statements - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents	$ 90,675	$ 48,154	$ 64,913	$ 63,364
Deposits with clearing organizations	67,678	42,222
Receivable from brokers, dealers and clearing organizations	166,493	187,115
Receivable from customers, net of allowance for credit losses of $886 ($769 in 2017)	720,777	848,226
Income tax receivable	1,014	2,939
Securities purchased under agreements to resell	290	658
Securities owned, at fair value	837,584	926,597
Notes receivable, net of accumulated amortization and allowance for uncollectibles of $25,109 and $6,800, respectively ($24,705 and $7,975, respectively, in 2017)	44,058	40,520
Office facilities, net of accumulated depreciation of $104,065 ($97,118 in 2013)	28,988	27,187
Subordinated loan receivable	0	0
Intangible assets	32,100	31,700
Goodwill	137,889	137,889
Other assets	112,768	145,310
Deferred tax assets	0	0
Investment in subsidiaries	0	0
Intercompany receivables	0	0
Total assets	2,240,314	2,438,517
Liabilities
Drafts payable	16,348	42,412
Bank call loans	15,000	118,300
Payable to brokers, dealers and clearing organizations	289,207	211,483
Payable to customers	336,616	385,907
Securities sold under agreements to repurchase	484,218	586,478
Securities sold but not yet purchased, at fair value	85,446	94,486
Accrued compensation	167,348	173,116
Accounts payable and other liabilities	87,630	92,495
Income tax payable	0	0
Senior secured notes, net of debt issuance costs of $904 ($1,163 in 2017)	199,096	198,837
Subordinated indebtedness	0	0
Deferred tax liabilities, net	14,083	11,092
Intercompany payables	0	0
Total liabilities	1,694,992	1,914,606
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	545,322	523,550
Non-controlling interest	0	361
Total stockholders' equity	545,322	523,911	513,334
Total liabilities and stockholders' equity	2,240,314	2,438,517
Allowance for credit losses	886	769
Amounts pledged	518,000	655,700
Notes Receivable, Net Accumulated Amortization	25,109	24,705
Notes Receivable, Net Allowance for Uncollectibles	6,800	7,975
Net accumulated depreciation	89,182	82,826
Unamortized debt issuance expense	904	1,163
Eliminations
ASSETS
Cash and cash equivalents	0	0	0	0
Deposits with clearing organizations	0	0
Receivable from brokers, dealers and clearing organizations	0	0
Receivable from customers, net of allowance for credit losses of $886 ($769 in 2017)	0	0
Income tax receivable	(67,508)	(69,084)
Securities purchased under agreements to resell	0	0
Securities owned, at fair value	0	0
Notes receivable, net of accumulated amortization and allowance for uncollectibles of $25,109 and $6,800, respectively ($24,705 and $7,975, respectively, in 2017)	0	0
Office facilities, net of accumulated depreciation of $104,065 ($97,118 in 2013)	0	0
Subordinated loan receivable	(112,558)	(112,558)
Intangible assets	0	0
Goodwill		0
Other assets	0	0
Deferred tax assets	(18,950)	(21,965)
Investment in subsidiaries	(1,208,541)	(1,130,571)
Intercompany receivables	(26,330)	(135,586)
Total assets	(1,433,887)	(1,469,764)
Liabilities
Drafts payable	0	0
Bank call loans	0	0
Payable to brokers, dealers and clearing organizations	0	0
Payable to customers	0	0
Securities sold under agreements to repurchase	0	0
Securities sold but not yet purchased, at fair value	0	0
Accrued compensation	0	0
Accounts payable and other liabilities	(9)	0
Income tax payable	(67,507)	(69,084)
Senior secured notes, net of debt issuance costs of $904 ($1,163 in 2017)	0	0
Subordinated indebtedness	(112,558)	(112,558)
Deferred tax liabilities, net	(18,946)	(21,965)
Intercompany payables	(26,334)	(135,586)
Total liabilities	(225,354)	(339,193)
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	(1,208,533)	(1,130,571)
Non-controlling interest		0
Total stockholders' equity	(1,208,533)	(1,130,571)
Total liabilities and stockholders' equity	(1,433,887)	(1,469,764)
Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	3,826	3,716	10,284	2,586
Deposits with clearing organizations	0	0
Receivable from brokers, dealers and clearing organizations	0	0
Receivable from customers, net of allowance for credit losses of $886 ($769 in 2017)	0	0
Income tax receivable	23,491	26,025
Securities purchased under agreements to resell	0	0
Securities owned, at fair value	1,358	1,386
Notes receivable, net of accumulated amortization and allowance for uncollectibles of $25,109 and $6,800, respectively ($24,705 and $7,975, respectively, in 2017)	0	0
Office facilities, net of accumulated depreciation of $104,065 ($97,118 in 2013)	20,722	20,221
Subordinated loan receivable	112,558	112,558
Intangible assets	400	0
Goodwill	0	0
Other assets	2,581	2,573
Deferred tax assets	455	0
Investment in subsidiaries	546,704	507,747
Intercompany receivables	46,840	83,437
Total assets	758,935	757,663
Liabilities
Drafts payable	0	0
Bank call loans	0	0
Payable to brokers, dealers and clearing organizations	0	0
Payable to customers	0	0
Securities sold under agreements to repurchase	0	0
Securities sold but not yet purchased, at fair value	0	0
Accrued compensation	0	0
Accounts payable and other liabilities	31,653	33,994
Income tax payable	22,189	22,189
Senior secured notes, net of debt issuance costs of $904 ($1,163 in 2017)	0	0
Subordinated indebtedness	0	0
Deferred tax liabilities, net	0	17
Intercompany payables	26,334	62,163
Total liabilities	80,176	118,363
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	678,759	639,300
Non-controlling interest		0
Total stockholders' equity	678,759	639,300
Total liabilities and stockholders' equity	758,935	757,663
Non-Guarantor Subsidiaries
ASSETS
Cash and cash equivalents	33,323	36,996	54,400	59,871
Deposits with clearing organizations	67,678	42,222
Receivable from brokers, dealers and clearing organizations	166,493	187,115
Receivable from customers, net of allowance for credit losses of $886 ($769 in 2017)	720,777	848,226
Income tax receivable	(702)	0
Securities purchased under agreements to resell	290	658
Securities owned, at fair value	836,226	925,211
Notes receivable, net of accumulated amortization and allowance for uncollectibles of $25,109 and $6,800, respectively ($24,705 and $7,975, respectively, in 2017)	44,058	40,520
Office facilities, net of accumulated depreciation of $104,065 ($97,118 in 2013)	8,266	6,966
Subordinated loan receivable	0	0
Intangible assets	31,700	31,700
Goodwill	137,889	137,889
Other assets	110,052	142,604
Deferred tax assets	18,494	18,463
Investment in subsidiaries	0	0
Intercompany receivables	(6,299)	0
Total assets	2,168,245	2,418,570
Liabilities
Drafts payable	16,348	42,412
Bank call loans	15,000	118,300
Payable to brokers, dealers and clearing organizations	289,207	211,483
Payable to customers	336,616	385,907
Securities sold under agreements to repurchase	484,218	586,478
Securities sold but not yet purchased, at fair value	85,446	94,486
Accrued compensation	167,348	173,116
Accounts payable and other liabilities	55,823	51,280
Income tax payable	42,878	44,455
Senior secured notes, net of debt issuance costs of $904 ($1,163 in 2017)	0	0
Subordinated indebtedness	112,558	112,558
Deferred tax liabilities, net	33,029	33,040
Intercompany payables	0	73,423
Total liabilities	1,638,471	1,926,938
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	529,774	491,271
Non-controlling interest		361
Total stockholders' equity	529,774	491,632
Total liabilities and stockholders' equity	2,168,245	2,418,570
Parent
ASSETS
Cash and cash equivalents	53,526	7,442	229	$ 907
Deposits with clearing organizations	0	0
Receivable from brokers, dealers and clearing organizations	0	0
Receivable from customers, net of allowance for credit losses of $886 ($769 in 2017)	0	0
Income tax receivable	45,733	45,998
Securities purchased under agreements to resell	0	0
Securities owned, at fair value	0	0
Notes receivable, net of accumulated amortization and allowance for uncollectibles of $25,109 and $6,800, respectively ($24,705 and $7,975, respectively, in 2017)	0	0
Office facilities, net of accumulated depreciation of $104,065 ($97,118 in 2013)	0	0
Subordinated loan receivable	0	0
Intangible assets	0	0
Goodwill	0	0
Other assets	135	133
Deferred tax assets	1	3,502
Investment in subsidiaries	661,837	622,824
Intercompany receivables	(14,211)	52,149
Total assets	747,021	732,048
Liabilities
Drafts payable	0	0
Bank call loans	0	0
Payable to brokers, dealers and clearing organizations	0	0
Payable to customers	0	0
Securities sold under agreements to repurchase	0	0
Securities sold but not yet purchased, at fair value	0	0
Accrued compensation	0	0
Accounts payable and other liabilities	163	7,221
Income tax payable	2,440	2,440
Senior secured notes, net of debt issuance costs of $904 ($1,163 in 2017)	199,096	198,837
Subordinated indebtedness	0	0
Deferred tax liabilities, net	0	0
Intercompany payables	0	0
Total liabilities	201,699	208,498
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	545,322	523,550	$ 510,703
Non-controlling interest		0
Total stockholders' equity	545,322	523,550
Total liabilities and stockholders' equity	$ 747,021	$ 732,048