Condensed Consolidated Statements of Financial Condition (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Cash and cash equivalents, restricted from use	$ 6.9	$ 7.3
Advisory fees receivable, allowance for doubtful accounts	0.1	0.1
Property and equipment, accumulated depreciation	$ 52.3	$ 50.2
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	36,399,052	35,775,557
Common stock, shares outstanding	28,768,414	28,647,312
Contingent convertible preferred stock, par value	$ 0.01	$ 0.01
Contingent convertible preferred stock, shares authorized	10,000,000	10,000,000
Contingent convertible preferred stock, shares issued	1,099,877	1,099,877
Contingent convertible preferred stock, shares outstanding	1,099,877	1,099,877
Exchangeable shares of subsidiary, shares issued	257,156	257,156
Exchangeable shares of subsidiary, shares outstanding	61,691	110,191
Treasury stock, par value	$ 0.01	$ 0.01
Treasury stock, shares	7,630,638	7,128,245