STATEMENT OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Statement [Abstract]
Net revenues	$ 640,624	$ 473,270	$ 307,707
Cost of net revenues	294,857	219,542	134,491
Gross profit	345,767	253,728	173,216
Operating expenses:
Technology and development	85,746	65,675	48,393
Sales and marketing	148,806	113,952	59,284
General and administrative	70,502	58,710	40,764
Total operating expenses	305,054	238,337	148,441
Income from operations	40,713	15,391	24,775
Interest expense	(597)	(64)	(42)
Interest and other income, net	42	35	482
Income before income taxes	40,158	15,362	25,215
Provision for income taxes	(17,160)	(1,314)	(8,088)
Net income	$ 22,998	$ 14,048	$ 17,127
Net income per share:
Basic (in dollars per share)	$ 0.64	$ 0.43	$ 0.63
Diluted (in dollars per share)	$ 0.61	$ 0.40	$ 0.59
Weighted average shares:
Basic	35,826	32,788	27,025
Diluted	37,432	35,007	29,249