Condensed Consolidated Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts receivable, allowance for doubtful accounts	$ 1,500	$ 475
Investments at fair value, cost basis	$ 116,531	$ 33,593
Treasury stock, shares	652,600	387,890
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	33,899,875	20,948,998
Common stock, shares outstanding	33,247,275	20,561,108
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	20,045,736	31,138,193
Common stock, shares outstanding	20,045,736	31,138,193