Consolidated Statements of Financial Condition (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fixed assets, accumulated depreciation and amortization	$ 23,852	$ 17,764
Intangible assets, accumulated amortization	$ 20,220	$ 8,146
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	5,346,003	0
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	119,393,640	75,490,209
Common stock, shares outstanding	114,047,637	75,490,209
Common stock, shares restricted	576,892	1,554,124
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