CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Agency revenues	$ 7,982,116	$ 6,527,898	$ 5,845,802
Merchant revenues	2,048,005	2,082,973	2,186,054
Advertising and other revenues	712,885	613,116	410,115
Total revenues	10,743,006	9,223,987	8,441,971
Cost of revenues	428,314	632,180	857,841
Gross profit	10,314,692	8,591,807	7,584,130
Operating expenses:
Performance advertising	3,479,287	2,738,218	2,334,453
Brand advertising	295,698	273,704	257,077
Sales and marketing	435,225	353,221	310,910
Personnel, including stock-based compensation of $249,574, $247,395, and $186,425, respectively	1,350,032	1,166,226	950,191
General and administrative	455,909	415,420	352,869
Information technology	142,393	113,617	97,498
Depreciation and amortization	309,135	272,494	207,820
Impairment of goodwill	940,700	0	0
Total operating expenses	7,408,379	5,332,900	4,510,818
Operating income	2,906,313	3,258,907	3,073,312
Other income (expense):
Interest income	94,946	55,729	13,933
Interest expense	(207,900)	(160,229)	(88,353)
Foreign currency transactions and other	(16,913)	(26,087)	(9,444)
Impairment of cost-method investments	(63,208)	0	0
Total other expense	(193,075)	(130,587)	(83,864)
Earnings before income taxes	2,713,238	3,128,320	2,989,448
Income tax expense	578,251	576,960	567,695
Net income	$ 2,134,987	$ 2,551,360	$ 2,421,753
Net income applicable to common stockholders per basic common share	$ 43.14	$ 50.09	$ 46.30
Weighted-average number of basic common shares outstanding	49,491	50,940	52,301
Net income applicable to common stockholders per diluted common share	$ 42.65	$ 49.45	$ 45.67
Weighted-average number of diluted common shares outstanding	50,063	51,593	53,023