Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Cash and cash equivalents, restricted from use	$ 9,689	$ 3,781
Advisory fees receivable, allowance for doubtful accounts	400	0
Property and equipment, accumulated depreciation	$ 46,600	$ 45,000
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)	46,755,222	45,001,788
Common stock, shares outstanding (shares)	19,759,779	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)	26,995,443	24,596,792