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Convertible Senior Notes - Due 2025 - Terms (Details) - 2025 Notes
May 08, 2018
USD ($)
D
item
$ / shares
Mar. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Convertible Senior Notes      
Face amount | $ $ 287,500,000 $ 287,500,000 $ 287,500,000
Interest rate (as a percent) 1.375%    
Net proceeds from offering | $ $ 279,100,000    
Offering costs | $ 8,400,000    
Principal multiple amount used in the conversion of the debt instrument | $ $ 1,000    
Convertible debt, conversion rate 18.6621    
Convertible debt, conversion price (in dollars per share) | $ / shares $ 53.58    
Trading day observation period used to determine the amount of cash and shares, if any, that are due upon conversion | item 25    
Convertible debt, equity component | $ $ 91,400,000    
Debt term 7 years    
At any time prior to close of business on the business day immediately preceding November 15, 2024      
Convertible Senior Notes      
Principal multiple amount used in the conversion of the debt instrument | $ $ 1,000    
Convertible debt, threshold, trading days | D 20    
Convertible debt, threshold, consecutive trading days | D 30    
Minimum percentage of common stock price as a percentage of the conversion price 130.00%    
Convertible debt, number of business days, measurement period | D 5    
Convertible debt, number of consecutive trading days, measurement period | D 10    
Trading price expressed as a percentage of the last reported sales price and conversion rate after the specified consecutive trading day period 98.00%    
On or after May 22, 2022      
Convertible Senior Notes      
Convertible debt, threshold, trading days | D 20    
Convertible debt, threshold, consecutive trading days | D 30    
Minimum percentage of common stock price as a percentage of the conversion price 130.00%