Condensed Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Cash and cash equivalents, restricted from use	$ 7,055	$ 7,170
Fees receivable, allowance for doubtful accounts	200	500
Property and equipment, accumulated depreciation	$ 19,000	$ 17,500
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)	50,471,753	48,701,743
Common stock, shares outstanding (shares)	19,231,494	19,001,605
Treasury stock, par value (usd per share)	$ 0.01	$ 0.01
Treasury stock, shares (shares)	31,240,259	29,700,138