Condensed Consolidated Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts receivable, allowance for doubtful accounts	$ 596	$ 1,149
Investments at fair value, cost basis	$ 33,598	$ 38,628
Treasury stock, shares	361,748	263,622
Class A common stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	20,894,035	20,536,740
Common stock, shares outstanding	20,532,287	20,273,118
Class B common stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	31,138,193	31,229,236
Common stock, shares outstanding	31,138,193	31,229,236