Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Net revenue	$ 392,960	$ 252,028	$ 1,081,326	$ 668,691
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)	53,395	33,778	145,043	89,278
Sales and marketing	133,172	83,168	364,865	224,792
Product development	106,223	72,730	282,503	179,903
General and administrative	61,767	33,194	160,776	89,022
Depreciation and amortization	33,767	23,122	91,766	55,552
Total costs and expenses	388,324	245,992	1,044,953	638,547
Income from operations	4,636	6,036	36,373	30,144
Other income (expense), net	156	672	(404)	228
Income before income taxes	4,792	6,708	35,969	30,372
Provision for income taxes	8,155	4,406	12,982	20,270
Net income (loss)	$ (3,363)	$ 2,302	$ 22,987	$ 10,102
Net income (loss) per share of common stock:
Basic (in dollars per share)	$ (0.03)	$ 0.02	$ 0.21	$ 0.10
Diluted (in dollars per share)	$ (0.03)	$ 0.02	$ 0.20	$ 0.09
Weighted-average shares used to compute net income (loss) per share:
Basic (in shares)	113,940	106,304	111,552	104,241
Diluted (in shares)	113,940	113,618	117,090	112,420