Condensed Consolidating Financial Information - Condensed Consolidating Balance Sheet (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents	$ 44,794,000	$ 64,913,000	$ 99,044,000	$ 63,364,000
Deposits with clearing organizations	44,201,000	38,185,000
Receivable from brokers, dealers and clearing organizations	248,891,000	214,934,000
Receivable from customers, net of allowance	775,602,000	847,386,000
Income tax receivable	5,061,000	5,816,000
Securities purchased under agreements to resell	0	24,006,000
Securities owned	1,037,463,000	707,108,000
Notes receivable, net of accumulated amortization and allowance for uncollectibles	38,241,000	30,099,000
Office facilities, net of accumulated depreciation	26,554,000	27,233,000
Subordinated loan receivable	0	0
Intangible assets	31,700,000	31,700,000
Goodwill	137,889,000	137,889,000
Other assets	118,005,000	107,661,000
Deferred tax assets	0	0
Investment in subsidiaries	0	0
Intercompany receivables	0	0
Total assets	2,508,401,000	2,236,930,000
Liabilities
Drafts payable	26,480,000	39,228,000
Bank call loans	130,100,000	145,800,000
Payable to brokers, dealers and clearing organizations	247,479,000	221,389,000
Payable to customers	396,515,000	449,946,000
Securities sold under agreements to repurchase	398,650,000	378,084,000
Securities sold but not yet purchased, at fair value	366,581,000	85,050,000
Accrued compensation	130,109,000	145,053,000
Accounts payable and other liabilities	91,534,000	96,557,000
Income tax payable	0	0
Senior secured notes, net of debt issuance costs of $1,199 ($648 in 2016)	198,801,000	149,352,000
Subordinated indebtedness	0	0
Deferred tax liabilities, net of deferred tax assets of $60,919 ($59,062 in 2016)	17,377,000	13,137,000
Intercompany payables	0	0
Total liabilities	2,003,626,000	1,723,596,000
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	504,418,000	510,703,000
Noncontrolling interest	357,000	2,631,000
Total stockholders' equity	504,775,000	513,334,000	516,012,000
Total liabilities and stockholders' equity	2,508,401,000	2,236,930,000
Allowance for credit losses	782,000	794,000
Amounts pledged	642,501,000	438,385,000
Net accumulated depreciation	87,861,000	84,073,000
Accumulated amortization	24,694,000	24,826,000
Accumulated allowance	7,519,000	6,784,000
Unamortized debt issuance expense	1,199,000	648,000
Deferred tax assets, gross	60,919,000	59,062,000
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	(71,524,000)	(64,469,000)
Securities purchased under agreements to resell		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	(112,558,000)	(112,558,000)
Intangible assets	0	0
Goodwill	0	0
Other assets	0	0
Deferred tax assets	(33,701,000)	(38,664,000)
Investment in subsidiaries	(1,075,501,000)	(1,068,390,000)
Intercompany receivables	(140,898,000)	(75,820,000)
Total assets	(1,434,182,000)	(1,359,901,000)
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	(71,524,000)	(64,469,000)
Senior secured notes, net of debt issuance costs of $1,199 ($648 in 2016)	0	0
Subordinated indebtedness	(112,558,000)	(112,558,000)
Deferred tax liabilities, net of deferred tax assets of $60,919 ($59,062 in 2016)	(33,701,000)	(38,664,000)
Intercompany payables	(140,898,000)	(75,820,000)
Total liabilities	(358,681,000)	(291,511,000)
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	(1,075,501,000)	(1,068,390,000)
Noncontrolling interest	0	0
Total stockholders' equity	(1,075,501,000)	(1,068,390,000)
Total liabilities and stockholders' equity	(1,434,182,000)	(1,359,901,000)
Parent Company [Member]
ASSETS
Cash and cash equivalents	507,000	229,000	302,000	907,000
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	48,052,000	41,996,000
Securities purchased under agreements to resell		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	140,000	71,000
Deferred tax assets	522,000	394,000
Investment in subsidiaries	598,256,000	584,767,000
Intercompany receivables	62,143,000	37,906,000
Total assets	709,620,000	665,363,000
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	3,961,000	2,868,000
Income tax payable	2,440,000	2,440,000
Senior secured notes, net of debt issuance costs of $1,199 ($648 in 2016)	198,801,000	149,352,000
Subordinated indebtedness	0	0
Deferred tax liabilities, net of deferred tax assets of $60,919 ($59,062 in 2016)	0	0
Intercompany payables	0	0
Total liabilities	205,202,000	154,660,000
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	504,418,000	510,703,000
Noncontrolling interest	0	0
Total stockholders' equity	504,418,000	510,703,000
Total liabilities and stockholders' equity	709,620,000	665,363,000
Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	11,963,000	10,284,000	30,379,000	2,586,000
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	28,533,000	28,289,000
Securities purchased under agreements to resell		0
Securities owned	1,268,000	23,227,000
Notes receivable, net of accumulated amortization and allowance for uncollectibles	0	0
Office facilities, net of accumulated depreciation	20,596,000	21,963,000
Subordinated loan receivable	112,558,000	112,558,000
Intangible assets	0	0
Goodwill	0	0
Other assets	2,472,000	2,598,000
Deferred tax assets	0	309,000
Investment in subsidiaries	477,245,000	483,623,000
Intercompany receivables	78,755,000	37,914,000
Total assets	733,390,000	720,765,000
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	34,522,000	34,920,000
Income tax payable	22,189,000	22,189,000
Senior secured notes, net of debt issuance costs of $1,199 ($648 in 2016)	0	0
Subordinated indebtedness	0	0
Deferred tax liabilities, net of deferred tax assets of $60,919 ($59,062 in 2016)	29,000	7,000
Intercompany payables	62,163,000	62,205,000
Total liabilities	118,903,000	119,321,000
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	614,487,000	601,444,000
Noncontrolling interest	0	0
Total stockholders' equity	614,487,000	601,444,000
Total liabilities and stockholders' equity	733,390,000	720,765,000
Non-Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	32,324,000	54,400,000	$ 68,363,000	$ 59,871,000
Deposits with clearing organizations	44,201,000	38,185,000
Receivable from brokers, dealers and clearing organizations	248,891,000	214,934,000
Receivable from customers, net of allowance	775,602,000	847,386,000
Income tax receivable	0	0
Securities purchased under agreements to resell		24,006,000
Securities owned	1,036,195,000	683,881,000
Notes receivable, net of accumulated amortization and allowance for uncollectibles	38,241,000	30,099,000
Office facilities, net of accumulated depreciation	5,958,000	5,270,000
Subordinated loan receivable	0	0
Intangible assets	31,700,000	31,700,000
Goodwill	137,889,000	137,889,000
Other assets	115,393,000	104,992,000
Deferred tax assets	33,179,000	37,961,000
Investment in subsidiaries	0	0
Intercompany receivables	0	0
Total assets	2,499,573,000	2,210,703,000
Liabilities
Drafts payable	26,480,000	39,228,000
Bank call loans	130,100,000	145,800,000
Payable to brokers, dealers and clearing organizations	247,479,000	221,389,000
Payable to customers	396,515,000	449,946,000
Securities sold under agreements to repurchase	398,650,000	378,084,000
Securities sold but not yet purchased, at fair value	366,581,000	85,050,000
Accrued compensation	130,109,000	145,053,000
Accounts payable and other liabilities	53,051,000	58,769,000
Income tax payable	46,895,000	39,840,000
Senior secured notes, net of debt issuance costs of $1,199 ($648 in 2016)	0	0
Subordinated indebtedness	112,558,000	112,558,000
Deferred tax liabilities, net of deferred tax assets of $60,919 ($59,062 in 2016)	51,049,000	51,794,000
Intercompany payables	78,735,000	13,615,000
Total liabilities	2,038,202,000	1,741,126,000
Stockholders' equity
Stockholders' equity attributable to Oppenheimer Holdings Inc.	461,014,000	466,946,000
Noncontrolling interest	357,000	2,631,000
Total stockholders' equity	461,371,000	469,577,000
Total liabilities and stockholders' equity	$ 2,499,573,000	$ 2,210,703,000