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Debt and Credit Arrangements - 2024 Notes (Details)
$ / shares in Units, shares in Thousands
1 Months Ended 12 Months Ended
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2020
USD ($)
day
$ / shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2019
USD ($)
Nov. 06, 2017
USD ($)
Oct. 31, 2017
$ / shares
Debt Instrument            
Share price (usd per share) | $ / shares   $ 117.79        
Long-term debt   $ 221,600,000   $ 761,000,000.0    
Convertible Debt | Convertible Notes, due 2024            
Debt Instrument            
Debt instrument stated interest rate (percent)   1.00%     1.00%  
Principal amount   $ 258,800,000   $ 258,800,000 $ 258,800,000  
Share conversion rate   0.0170285        
Debt instrument, conversion price (usd per share) | $ / shares   $ 58.725        
Debt instrument, conversion premium (percentage)   35.00%        
Share price (usd per share) | $ / shares           $ 43.50
Value of securities above principal amount of debt if converted   $ 260,200,000        
Debt instrument, threshold for trading days | day   20        
Debt instrument, threshold for consecutive trading days | day   30        
Applicable conversion price threshold (as percentage)   130.00%        
Maximum days after five trading days   5 days        
Applicable conversion price, less than (as percentage)   97.00%        
Trigger price (usd per share) | $ / shares   $ 76.3425        
Debt instrument effective interest rate         4.80%  
Non cash payment for derivative instrument $ 59,500,000          
Number of shares underlying warrant (shares) | shares 4,410   4,410      
Proceeds from issuance of warrants     $ 46,000,000.0      
Percentage above previous sales price           65.00%
Net cost of convertible note hedge and warrant   $ 13,500,000        
Convertible Debt | Convertible Notes, due 2024 | Maximum            
Debt Instrument            
Debt instrument, conversion price (usd per share) | $ / shares   $ 71.775       $ 71.775
Convertible Debt | Convertible Notes, due 2024 | Liability Component            
Debt Instrument            
Principal amount         $ 200,100,000  
Long-term debt   $ 220,900,000        
Debt issuance costs         5,300,000  
Convertible Debt | Convertible Notes, due 2024 | Equity Component            
Debt Instrument            
Principal amount         58,700,000  
Debt issuance costs         $ 1,500,000