Other Balance Sheet Items (Other Current Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Prepaid registry fees, current	$ 20,450
Prepaid expenses	17,296	$ 15,787
Accounts Receivable, Net	6,117	5,111
Income Taxes Receivable, Current	3,996	6,347
Other Assets, Miscellaneous, Current	4,207	4,157
Other Assets, Current	$ 52,066	$ 31,402