Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts receivable, allowance for doubtful accounts	$ 475	$ 1,149
Investments at fair value, cost basis	$ 33,593	$ 38,628
Treasury stock, shares	387,890	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	20,948,998	20,536,740
Common stock, shares outstanding	20,561,108	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