Revenue from Contracts with Customers - Disaggregation of Revenue (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) division	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) division	Sep. 30, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Revenue	$ 792,845	$ 709,912	$ 2,351,862	$ 2,121,494
Number of divisions | division	2		2
Web Division
Disaggregation of Revenue [Line Items]
Revenue	$ 418,064	387,662	$ 1,228,401	1,139,422
Media and Carrier Division
Disaggregation of Revenue [Line Items]
Revenue	374,781	322,250	1,123,461	982,072
U.S.
Disaggregation of Revenue [Line Items]
Revenue	437,381	413,116	1,309,979	1,248,175
International
Disaggregation of Revenue [Line Items]
Revenue	$ 355,464	$ 296,796	$ 1,041,883	$ 873,319