Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income Statement [Abstract]
Net revenue	$ 324,705	$ 188,456
Costs and expenses:
Cost of revenue (exclusive of depreciation and amortization shown separately below)	42,384	25,133
Sales and marketing	109,417	65,884
Product development	80,672	47,093
General and administrative	42,784	24,854
Depreciation and amortization	25,806	14,882
Total costs and expenses	301,063	177,846
Income from operations	23,642	10,610
Other income (expense), net	(308)	224
Income before income taxes	23,334	10,834
Provision for income taxes	718	5,845
Net income	$ 22,616	$ 4,989
Net income per share of common stock:
Basic (in dollars per share)	$ 0.21	$ 0.05
Diluted (in dollars per share)	$ 0.20	$ 0.04
Weighted-average shares used to compute net income per share:
Basic (in shares)	109,445	102,210
Diluted (in shares)	115,398	111,310