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Long-term Debt - Convertible Senior Notes Due 2025 (Details)
3 Months Ended
May 14, 2018
USD ($)
day
Dec. 31, 2018
USD ($)
$ / shares
Oct. 01, 2018
$ / shares
Debt Instrument [Line Items]      
Principal amount | $   $ 513,647,000  
Share price (usd per share) | $ / shares     $ 10.51
Senior Notes | 2025 Convertible Notes      
Debt Instrument [Line Items]      
Stated interest rate 2.375%    
Principal amount | $ $ 172,500,000 172,500,000  
Semi-annual stated rate 2.375%    
Carrying amount of equity component | $   $ 39,000,000.0  
Effective interest rate   9.00%  
Conversion rate per $1000 principal amount 62.8931    
Conversion price, per share (in dollars per share) | $ / shares   $ 15.90  
Share price (usd per share) | $ / shares   $ 15.90  
Debt Conversion, Condition One | Senior Notes | 2025 Convertible Notes      
Debt Instrument [Line Items]      
Trading days | day 20    
Consecutive trading days | day 30