UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Agency revenues	$ 1,582,153	$ 1,474,396	$ 2,781,501	$ 2,515,540
Merchant revenues	546,013	567,253	1,040,688	1,094,251
Advertising and other revenues	152,231	81,926	298,902	155,586
Total revenues	2,280,397	2,123,575	4,121,091	3,765,377
Cost of revenues	187,491	240,579	355,949	475,910
Gross profit	2,092,906	1,882,996	3,765,142	3,289,467
Operating expenses:
Advertising — Online	770,818	639,655	1,414,034	1,160,503
Advertising — Offline	66,303	58,026	129,885	111,500
Sales and marketing	94,523	75,053	176,467	139,364
Personnel, including stock-based compensation of $60,164, $35,168, $114,172 and $73,971, respectively	289,156	221,852	548,140	416,383
General and administrative	98,945	91,067	199,123	164,048
Information technology	27,156	24,042	52,517	47,266
Depreciation and amortization	67,674	40,287	132,676	78,663
Total operating expenses	1,414,575	1,149,982	2,652,842	2,117,727
Operating income	678,331	733,014	1,112,300	1,171,740
Other income (expense):
Interest income	13,037	1,634	24,633	2,675
Interest expense	(41,547)	(17,106)	(75,026)	(34,851)
Foreign currency transactions and other	(1,444)	(1,777)	(6,287)	(7,746)
Total other income (expense)	(29,954)	(17,249)	(56,680)	(39,922)
Earnings before income taxes	648,377	715,765	1,055,620	1,131,818
Income tax expense	131,345	139,314	205,261	224,149
Net income	$ 517,032	$ 576,451	$ 850,359	$ 907,669
Net income applicable to common stockholders per basic common share	$ 10.02	$ 11.00	$ 16.43	$ 17.36
Weighted-average number of basic common shares outstanding	51,589	52,397	51,748	52,275
Net income applicable to common stockholders per diluted common share	$ 9.94	$ 10.89	$ 16.27	$ 17.12
Weighted-average number of diluted common shares outstanding	52,038	52,955	52,253	53,004