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Notes Payable Schedule of Outstanding Balance on Convertible Notes (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Aug. 14, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Net carrying amount $ 166,006   $ 0
Convertible debt | 3.00% Convertible notes      
Debt Instrument [Line Items]      
Principal 305,000 $ 305,000  
Debt discount and issuance cost, net (138,994)    
Net carrying amount 166,006 166,300  
Equity component: $ 134,450 $ 138,700