Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at Beginning of Period	$ 15,056
Charged to Cost and Expenses	47,110
Deductions	(50,620)
Balance at End of Period	11,546
Balance as of December 31, 2017	684,119
Recognition of unearned revenue	(3,669,340)
Deferral of revenue	3,669,999
Balance as of June 30, 2018	$ 684,119	$ 684,778
Remaining performance obligations	true