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Debt - Convertible Senior Notes (Details)
$ / shares in Units, $ in Millions
Aug. 07, 2017
USD ($)
$ / shares
shares
Sep. 30, 2017
$ / shares
Aug. 01, 2017
$ / shares
Common stock      
Debt      
Share Price | $ / shares     $ 13.28
Convertible senior notes | 2025 Notes | Over-Allotment Option      
Debt      
Loan amount $ 17.5    
Convertible senior notes | 2025 Notes | Private Placement      
Debt      
Loan amount $ 192.5    
Interest rate (as a percent) 2.50%    
Convertible senior notes | 2025 Notes | Common stock      
Debt      
Conversion rate 57.9240    
Conversion price (dollars per share) | $ / shares $ 17.26 $ 17.26  
Conversion premium (as a percent) 30.00%    
Number of shares repurchased and retired | shares 1,317,771    
Value of shares repurchased and retired $ 17.5