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Debt - Convertible Senior Notes (Details) - USD ($)
 3 Months Ended 6 Months Ended
Aug. 12, 2014
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Debt Instrument [Line Items]            
Face amount of debt   $ 1,127,750,000   $ 1,127,750,000   $ 259,000,000
Fair value of debt   1,104,041,000   1,104,041,000   255,291,000
Unamortized debt issuance costs   23,709,000   23,709,000   3,709,000
Net carrying value   226,998,000   226,998,000   226,291,000
2019 Notes            
Debt Instrument [Line Items]            
Face amount of debt $ 230,000,000.0 230,000,000   $ 230,000,000   230,000,000
Interest rate (as a percent) 0.75%          
Long term debt, unamortized debt issuance costs $ 7,100,000          
Conversion ratio 0.0188072     0.0188072    
Conversion price (in dollars per share) $ 53.17          
Repurchase price, expressed as a percentage of principal of debt repurchased 100.00%          
Fair value of debt   $ 217,400,000   $ 217,400,000    
Effective interest rate   1.38%   1.38%    
Additional interest for non-compliance       0.25%    
Second additional interest for non-compliance       0.50%    
Contractual interest expense   $ 432,000 $ 432,000 $ 863,000 $ 863,000  
Contingent interest expense   0 $ 0 288,000 $ 0  
Principal amount $ 230,000,000 230,000,000   230,000,000   230,000,000
Unamortized debt issuance costs   3,002,000   3,002,000   3,709,000
Net carrying value   $ 226,998,000   $ 226,998,000   $ 226,291,000