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Debt - Narrative (Details)
shares in Millions
1 Months Ended 3 Months Ended
Apr. 30, 2017
USD ($)
shares
Mar. 31, 2017
USD ($)
Mar. 21, 2017
USD ($)
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]        
Long-term debt, par value   $ 1,189,500,000   $ 1,189,500,000
Revolving credit facility   $ 150,000,000   0
Convertible Senior Notes        
Debt Instrument [Line Items]        
Stated interest rate (in hundredths)   5.00%    
Long-term debt, par value   $ 145,000,000   145,000,000
Convertible Senior Notes | 2% Convertible Senior Notes        
Debt Instrument [Line Items]        
Stated interest rate (in hundredths)   2.00%    
Convertible Senior Notes | 2% Convertible Senior Notes | Subsequent Event        
Debt Instrument [Line Items]        
Shares issued during period upon conversion of convertible debt (in shares) | shares 29.1      
2% Notes        
Debt Instrument [Line Items]        
Stated interest rate (in hundredths)   2.00%    
Long-term debt, par value   $ 207,600,000   207,600,000
Conversion rate (in shares per $1,000 note)   0.1438332    
2% Notes | Subsequent Event        
Debt Instrument [Line Items]        
Principal amount of notes converted into shares $ 202,500,000      
Principal amount of notes redeemed for cash $ 5,100,000      
Line of Credit | Revolving Credit Facility        
Debt Instrument [Line Items]        
Maximum borrowing capacity     $ 175,000,000  
Revolving credit facility   $ 150,000,000    
9% Debentures        
Debt Instrument [Line Items]        
Stated interest rate (in hundredths)   9.00%    
Long-term debt, par value   $ 256,900,000   $ 256,900,000
Conversion rate (in shares per $1,000 note)   0.0740741