Cash, Cash Equivalents and Restricted Cash - (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash	$ 1,867,506	$ 2,072,296
Non-current Assets (1)	4,531	4,367
Fair Value, Measurements, Recurring | Level 1 Securities | Money market funds
Cash and Cash Equivalents [Line Items]
Money market funds	726,160	449,734
Fair Value, Measurements, Recurring | Level 2 Securities
Cash and Cash Equivalents [Line Items]
Time Deposits		300,765
Money market funds | Fair Value, Measurements, Recurring | Level 1 Securities
Cash and Cash Equivalents [Line Items]
Non-current Assets (1)	$ 1,280	1,276
Bank Time Deposits | Fair Value, Measurements, Recurring | Level 2 Securities
Cash and Cash Equivalents [Line Items]
Non-current Assets (1)		$ 0