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Basis of Presentation and Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]        
Cash and cash equivalents $ 258,195 $ 122,899    
Current portion of restricted cash and cash equivalents 3,883 3,883    
Noncurrent restricted cash and cash equivalents 750,000 0    
Total cash, cash equivalents, and restricted cash at the end of period $ 1,012,078 $ 126,782 $ 291,271 $ 90,893