Nature of Expenses Allocated by Function - Cost of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Income and Expenses [Abstract]
Traffic acquisition costs	$ (1,068,911)	$ (789,152)	$ (585,492)
Other cost of revenue	(85,260)	(62,201)	(47,948)
Hosting costs	(41,978)	(30,428)	(24,780)
Depreciation and amortization	(38,469)	(29,866)	(21,455)
Data acquisition	(122)	(257)	(600)
Other cost of sales	(4,691)	(1,650)	(1,113)
Total cost of revenue	$ (1,154,171)	$ (851,353)	$ (633,440)