Earnings Per Share - Summary of Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Earnings Per Share [Abstract]
Basic weighted average number of shares outstanding (in shares)	13,630,368		13,604,276		13,595,458		13,606,527
Net dilutive effect of share-based awards, treasury method	667,074	[1]	567,526	[1]	621,789	[1]	503,604	[1]
Diluted weighted average number of shares outstanding (in shares)	14,297,442		14,171,802		14,217,247		14,110,131
Net income for the period	$ 4,625		$ 5,508		$ 6,792		$ 12,467
Net income attributable to non-controlling interest, net of tax	155		271		652		719
Net income attributable to Oppenheimer Holdings Inc.	$ 4,470		$ 5,237		$ 6,140		$ 11,748
Basic earnings (loss) per share (in dollars per share)	$ 0.33		$ 0.38		$ 0.45		$ 0.86
Diluted earnings (loss) per share (in dollars per share)	$ 0.31		$ 0.37		$ 0.43		$ 0.83

[1] For both the three and nine months ended September 30, 2014, the diluted earnings per share computation does not include the anti-dilutive effect of 58,008 shares of Class A Stock granted under share-based compensation arrangements (57,573 shares of Class A Stock granted under share-based compensation arrangements for the three and nine months ended September 30, 2013).