Balance Sheet Components (Property and Equipment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and Equipment [Abstract]
Property and equipment	$ 222,992	$ 163,803	$ 222,992	$ 163,803
Less: Accumulated depreciation and amortization	(130,325)	(109,680)	(130,325)	(109,680)
Net property and equipment	92,667	54,123	92,667	54,123
Depreciation and amortization expense	29,424	22,316	29,424	22,316	23,429
Computer and Other Equipment [Member]
Property and Equipment [Abstract]
Property and equipment	135,181	102,061	135,181	102,061
Software [Member]
Property and Equipment [Abstract]
Property and equipment	17,342	12,579	17,342	12,579
Leasehold Improvements [Member]
Property and Equipment [Abstract]
Property and equipment	11,009	9,559	11,009	9,559
Building Construction-in-Progress [Member]
Property and Equipment [Abstract]
Property and equipment	6,372	0	6,372	0
Furniture and Fixtures [Member]
Property and Equipment [Abstract]
Property and equipment	4,075	3,762	4,075	3,762
Capitalized software and website development costs [Member]
Property and Equipment [Abstract]
Property and equipment	49,013	35,842	49,013	35,842
Net property and equipment	21,857	16,923	21,857	16,923
Depreciation and amortization expense			$ 8,352	$ 5,371	$ 4,207