Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents	$ 116,582	$ 64,913	$ 107,537	$ 63,364
Deposits with clearing organizations	40,685	38,185
Receivable from brokers, dealers and clearing organizations	224,706	214,934
Receivable from customers, net of allowance	873,815	847,386
Income tax receivable	10,105	5,816
Securities purchased under agreements to resell, $3,617 at fair value	4,852	24,006
Securities owned	986,432	707,108
Notes receivable, net of accumulated amortization and allowance for uncollectibles	36,240	30,099
Office facilities, net of accumulated depreciation	26,525	27,233
Subordinated loan receivable	0	0
Intangible assets	31,700	31,700
Goodwill	137,889	137,889
Other assets	117,988	107,661
Deferred tax assets	0	0
Investment in subsidiaries	0	0
Intercompany receivables	0	0
Total assets	2,607,519	2,236,930
Liabilities
Drafts payable	29,767	39,228
Bank call loans	230,400	145,800
Payable to brokers, dealers and clearing organizations	239,578	221,389
Payable to customers	498,562	449,946
Securities sold under agreements to repurchase	457,809	378,084
Securities sold but not yet purchased, at fair value	234,778	85,050
Accrued compensation	113,088	145,053
Accounts payable and other liabilities	89,065	96,557
Income tax payable	0	0
Senior secured notes	198,896	149,352
Subordinated indebtedness	0	0
Deferred tax liabilities	14,462	13,137
Intercompany payables	0	0
Total liabilities	2,106,405	1,723,596
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	499,200	510,703
Noncontrolling interest	1,914	2,631
Total stockholders' equity	501,114	513,334	522,112
Total liabilities and stockholders' equity	2,607,519	2,236,930
Allowance for credit losses	790	794
Securities purchased under agreements to resell, fair value	3,617	24,006
Amounts pledged	644,359	438,385
Net accumulated depreciation	86,502	84,073
Accumulated amortization	23,735	24,826
Accumulated allowance	7,445	6,784
Unamortized debt issuance expense	1,104	648
Deferred tax assets, gross	61,296	59,062
Eliminations [Member]
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	0	0
Income tax receivable	(64,533)	(64,469)
Securities purchased under agreements to resell, $3,617 at fair value	0	0
Securities owned	0	0
Notes receivable, net of accumulated amortization and allowance for uncollectibles	0	0
Office facilities, net of accumulated depreciation	0	0
Subordinated loan receivable	(112,558)	(112,558)
Intangible assets	0	0
Goodwill	0	0
Other assets	0	0
Deferred tax assets	(35,530)	(38,664)
Investment in subsidiaries	(1,065,465)	(1,068,390)
Intercompany receivables	(78,365)	(75,820)
Total assets	(1,356,451)	(1,359,901)
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	0	0
Income tax payable	(64,533)	(64,469)
Senior secured notes	0	0
Subordinated indebtedness	(112,558)	(112,558)
Deferred tax liabilities	(35,530)	(38,664)
Intercompany payables	(78,365)	(75,820)
Total liabilities	(290,986)	(291,511)
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	(1,065,465)	(1,068,390)
Noncontrolling interest	0	0
Total stockholders' equity	(1,065,465)	(1,068,390)
Total liabilities and stockholders' equity	(1,356,451)	(1,359,901)
Parent Company [Member]
ASSETS
Cash and cash equivalents	73,653	229	606	907
Deposits with clearing organizations	0	0
Receivable from brokers, dealers and clearing organizations	0	0
Receivable from customers, net of allowance	0	0
Income tax receivable	46,208	41,996
Securities purchased under agreements to resell, $3,617 at fair value	0	0
Securities owned	0	0
Notes receivable, net of accumulated amortization and allowance for uncollectibles	0	0
Office facilities, net of accumulated depreciation	0	0
Subordinated loan receivable	0	0
Intangible assets	0	0
Goodwill	0	0
Other assets	108	71
Deferred tax assets	808	394
Investment in subsidiaries	588,206	584,767
Intercompany receivables	0	37,906
Total assets	708,983	665,363
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	1,226	2,868
Income tax payable	2,440	2,440
Senior secured notes	198,896	149,352
Subordinated indebtedness	0	0
Deferred tax liabilities	0	0
Intercompany payables	7,221	0
Total liabilities	209,783	154,660
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	499,200	510,703
Noncontrolling interest	0	0
Total stockholders' equity	499,200	510,703
Total liabilities and stockholders' equity	708,983	665,363
Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	3,232	10,284	525	2,586
Deposits with clearing organizations	0	0
Receivable from brokers, dealers and clearing organizations	0	0
Receivable from customers, net of allowance	0	0
Income tax receivable	28,430	28,289
Securities purchased under agreements to resell, $3,617 at fair value	0	0
Securities owned	1,275	23,227
Notes receivable, net of accumulated amortization and allowance for uncollectibles	0	0
Office facilities, net of accumulated depreciation	20,834	21,963
Subordinated loan receivable	112,558	112,558
Intangible assets	0	0
Goodwill	0	0
Other assets	1,638	2,598
Deferred tax assets	0	309
Investment in subsidiaries	477,259	483,623
Intercompany receivables	78,365	37,914
Total assets	723,591	720,765
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	34,163	34,920
Income tax payable	22,189	22,189
Senior secured notes	0	0
Subordinated indebtedness	0	0
Deferred tax liabilities	25	7
Intercompany payables	62,163	62,205
Total liabilities	118,540	119,321
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	605,051	601,444
Noncontrolling interest	0	0
Total stockholders' equity	605,051	601,444
Total liabilities and stockholders' equity	723,591	720,765
Non-Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	39,697	54,400	$ 106,406	$ 59,871
Deposits with clearing organizations	40,685	38,185
Receivable from brokers, dealers and clearing organizations	224,706	214,934
Receivable from customers, net of allowance	873,815	847,386
Income tax receivable	0	0
Securities purchased under agreements to resell, $3,617 at fair value	4,852	24,006
Securities owned	985,157	683,881
Notes receivable, net of accumulated amortization and allowance for uncollectibles	36,240	30,099
Office facilities, net of accumulated depreciation	5,691	5,270
Subordinated loan receivable	0	0
Intangible assets	31,700	31,700
Goodwill	137,889	137,889
Other assets	116,242	104,992
Deferred tax assets	34,722	37,961
Investment in subsidiaries	0	0
Intercompany receivables	0	0
Total assets	2,531,396	2,210,703
Liabilities
Drafts payable	29,767	39,228
Bank call loans	230,400	145,800
Payable to brokers, dealers and clearing organizations	239,578	221,389
Payable to customers	498,562	449,946
Securities sold under agreements to repurchase	457,809	378,084
Securities sold but not yet purchased, at fair value	234,778	85,050
Accrued compensation	113,088	145,053
Accounts payable and other liabilities	53,676	58,769
Income tax payable	39,904	39,840
Senior secured notes	0	0
Subordinated indebtedness	112,558	112,558
Deferred tax liabilities	49,967	51,794
Intercompany payables	8,981	13,615
Total liabilities	2,069,068	1,741,126
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	460,414	466,946
Noncontrolling interest	1,914	2,631
Total stockholders' equity	462,328	469,577
Total liabilities and stockholders' equity	$ 2,531,396	$ 2,210,703