Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenues	$ 11,692,713	$ 8,830,669	$ 6,779,511
Cost of revenues	7,659,666	6,029,901	4,591,476
Marketing	1,278,022	991,078	824,092
Technology and development	1,052,778	852,098	650,788
General and administrative	863,568	577,799	407,329
Operating income	838,679	379,793	305,826
Other income (expense):
Interest expense	(238,204)	(150,114)	(132,716)
Interest and other income (expense)	(115,154)	30,828	(31,225)
Income before income taxes	485,321	260,507	141,885
Provision for (benefit from) income taxes	(73,608)	73,829	19,244
Net income	$ 558,929	$ 186,678	$ 122,641
Earnings per share:
Basic (in USD per share)	$ 1.29	$ 0.44	$ 0.29
Diluted (in USD per share)	$ 1.25	$ 0.43	$ 0.28
Weighted-average common shares outstanding:
Basic (in shares)	431,885	428,822	425,889
Diluted (in shares)	446,814	438,652	436,456