Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Restricted cash - letters of credit	$ 9,800	$ 3,800
Advisory fees, allowance for credit loss	1,100	0
Accumulated depreciation and amortization	$ 47,735	$ 45,032
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (shares)	100,000,000	100,000,000
Common stock, shares issued (shares)	46,801,812	45,001,788
Common stock, shares outstanding (shares)	18,355,907	20,404,996
Exchangeable shares of subsidiary, shares issued (shares)	257,156	257,156
Exchangeable shares of subsidiary, shares outstanding (shares)	0	32,804
Treasury stock, par value (usd per share)	$ 0.01	$ 0.01
Treasury stock, shares (shares)	28,445,905	24,596,792