Property, Equipment and Software, Net (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	$ 167,308,000		$ 66,427,000
accumulated depreciation and amortization	(46,236,000)		(14,627,000)
Property, equipment and software, net	121,072,000		51,800,000
Capital lease, computer hardware	1,100,000
Depreciation and amortization on property, equipment and software capitalization	35,900,000		12,800,000	1,900,000
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	12,853,000		8,579,000
Property, Plant and Equipment, Useful Life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	28,778,000		14,999,000
Property, Plant and Equipment, Useful Life	5 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	6,804,000		4,695,000
Software [Member]
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	14,480,000		7,744,000
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	67,862,000	[1]	25,617,000
Property, Plant and Equipment, Useful Life	3 years
Software Development [Member]
Property, Plant and Equipment [Line Items]
property, equipment and software capitalization, gross	$ 36,531,000		$ 4,793,000

[1] (1)Includes computer hardware acquired under capital leases of $1.1 million as of December 31, 2012.