Condensed Consolidated Statements of Financial Condition (Parenthetical) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Fixed assets, accumulated depreciation and amortization	$ 25,466	$ 23,852
Intangible assets, accumulated amortization	$ 20,718	$ 20,220
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Treasury stock, shares	5,696,472	5,346,003
Common Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	119,672,938	119,393,640
Common stock, shares outstanding	113,976,466	114,047,637
Common stock, shares restricted	461,359	576,892
Common Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0