Revenue from Contracts with Customers - Disaggregation of Revenue (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) division	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) division	Jun. 30, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Revenue	$ 794,715	$ 705,074	$ 1,559,017	$ 1,411,582
Number of divisions | division	2		2
Web Division
Disaggregation of Revenue [Line Items]
Revenue	$ 404,342	377,558	$ 810,337	751,760
Media and Carrier Division
Disaggregation of Revenue [Line Items]
Revenue	390,373	327,516	748,680	659,822
U.S.
Disaggregation of Revenue [Line Items]
Revenue	443,668	416,859	872,598	835,059
International
Disaggregation of Revenue [Line Items]
Revenue	$ 351,047	$ 288,215	$ 686,419	$ 576,523