CONSOLIDATED STATEMENTS OF OPERATIONS (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Agency revenues	$ 4,410,689	$ 3,142,815	$ 2,339,253
Merchant revenues	2,211,474	2,104,752	2,004,432
Advertising and other revenues	171,143	13,389	11,925
Total revenues	6,793,306	5,260,956	4,355,610
Cost of revenues	1,077,420	1,177,275	1,275,730
Gross profit	5,715,886	4,083,681	3,079,880
Operating expenses:
Advertising - Online	1,798,645	1,273,637	919,214
Advertising - Offline	127,459	35,492	35,470
Sales and marketing	235,817	195,934	162,690
Personnel, including stock-based compensation of $140,526, $71,565 and $65,724, respectively	698,692	466,828	352,295
General and administrative	252,994	173,171	123,652
Information technology	71,890	43,685	33,813
Depreciation and amortization	117,975	65,141	53,824
Total operating expenses	3,303,472	2,253,888	1,680,958
Operating income	2,412,414	1,829,793	1,398,922
Other income (expense):
Interest income	4,167	3,860	8,119
Interest expense	(83,289)	(62,064)	(31,721)
Foreign currency transactions and other	(36,755)	(9,720)	(7,526)
Total other income (expense)	(115,877)	(67,924)	(31,128)
Earnings before income taxes	2,296,537	1,761,869	1,367,794
Income Tax Expense	403,739	337,832	308,663
Net income	1,892,798	1,424,037	1,059,131
Less: net income attributable to noncontrolling interests	135	4,471	2,760
Net income applicable to common stockholders	$ 1,892,663	$ 1,419,566	$ 1,056,371
Net income applicable to common stockholders per basic common share (in dollars per share)	$ 37.17	$ 28.48	$ 21.27
Weighted average number of basic common shares outstanding (in shares)	50,924	49,840	49,654
Net income applicable to common stockholders per diluted common share (in dollars per share)	$ 36.11	$ 27.66	$ 20.63
Weighted average number of diluted common shares outstanding (in shares)	52,413	51,326	51,211