Commitments And Contingencies (Narrative) (Details) number in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Commitments And Contingencies [Line Items]
Number of domain names registered	126.9
Uncertain tax positions	$ 212,000,000
ICANN Agreement [Member]
Commitments And Contingencies [Line Items]
Expiration Date of Registry Agreement	Nov. 30, 2024
Registry fee per transaction	$ 0.25
Payments for registry fees	31,500,000	$ 30,900,000	$ 28,400,000
.TV Agreement [Member]
Commitments And Contingencies [Line Items]
renewed agreement fees	$ 5,000,000	$ 5,000,000	$ 4,500,000