CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
ASSETS
Investment in GBL stock	$ 60.4	$ 48.9
Equity:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, shares outstanding (in shares)	22,058,000	22,274,000
Treasury stock, shares outstanding (in shares)	3,534,085	3,318,127
Class A [Member]
Equity:
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	6,629,254	6,629,254
Common stock, shares outstanding (in shares)	3,095,169	3,311,127
Class B [Member]
Equity:
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	19,196,792	19,196,792
Common stock, shares outstanding (in shares)	18,962,918	18,962,918