UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Agency revenues	$ 2,892,449	$ 2,345,673	$ 6,245,439	$ 5,127,174
Merchant revenues	620,290	596,503	1,608,189	1,637,191
Advertising and other revenues	177,813	160,725	540,945	459,627
Total revenues	3,690,552	3,102,901	8,394,573	7,223,992
Cost of revenues	101,489	155,619	356,242	511,568
Gross profit	3,589,063	2,947,282	8,038,331	6,712,424
Operating expenses:
Performance advertising	1,040,149	784,729	2,740,821	2,176,963
Brand advertising	72,792	67,858	254,958	219,543
Sales and marketing	124,865	93,069	322,710	269,536
Personnel, including stock-based compensation of $54,074, $58,274, $175,050 and $172,446, respectively	347,610	305,329	988,615	853,469
General and administrative	114,586	109,706	340,273	308,829
Information technology	36,389	28,830	104,974	81,347
Depreciation and amortization	78,745	69,054	229,328	201,730
Impairment of goodwill	940,700	0	940,700	0
Total operating expenses	2,755,836	1,458,575	5,922,379	4,111,417
Operating income	833,227	1,488,707	2,115,952	2,601,007
Other income (expense):
Interest income	24,218	14,682	65,857	39,315
Interest expense	(55,480)	(41,436)	(152,664)	(116,462)
Foreign currency transactions and other	(4,431)	(5,783)	(15,362)	(12,070)
Impairment of cost-method investments	0	0	(63,208)	0
Total other expense	(35,693)	(32,537)	(165,377)	(89,217)
Earnings before income taxes	797,534	1,456,170	1,950,575	2,511,790
Income tax expense	291,517	259,438	489,496	464,699
Net income	$ 506,017	$ 1,196,732	$ 1,461,079	$ 2,047,091
Net income applicable to common stockholders per basic common share	$ 10.24	$ 23.67	$ 29.49	$ 39.87
Weighted-average number of basic common shares outstanding	49,420	50,550	49,548	51,344
Net income applicable to common stockholders per diluted common share	$ 10.13	$ 23.41	$ 29.19	$ 39.40
Weighted-average number of diluted common shares outstanding	49,975	51,130	50,048	51,952