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Debt - Convertible Senior Notes and Capped Call (Details)
$ / shares in Units, shares in Millions
1 Months Ended 6 Months Ended
May 31, 2018
USD ($)
day
$ / shares
Jun. 30, 2018
USD ($)
$ / shares
shares
Debt Instrument [Line Items]    
Conversion price on convertible debt (in USD per share) | $ / shares   $ 40.82
Payment on debt issuance cost   $ 7,946,000
Convertible debt | Convertible Senior Notes    
Debt Instrument [Line Items]    
Stated interest rate on debt 0.125%  
Proceeds from issuance of debt $ 250,700,000  
Conversion ratio on convertible debt 0.0244978  
Conversion price on convertible debt (in USD per share) | $ / shares $ 40.82  
Sinking fund payment $ 0  
Conversion option   63,756,000
Effective interest rate on debt 6.39%  
Payment on debt issuance cost $ 8,100,000  
Debt issuance costs $ 6,100,000 $ 5,961,000
Cap price of the Capped Call Transactions (in dollars per share) | $ / shares $ 62.80  
Number of shares covered in the Capped Call Transactions | shares   6.3
Cost of Capped Call Transactions recorded in additional paid in capital   $ 31,412,000
Convertible debt | Convertible Senior Notes | Fundamental change event    
Debt Instrument [Line Items]    
Debt redemption price as percentage of principal amount 100.00%  
Convertible debt | Convertible Senior Notes | On or after May 5, 2021    
Debt Instrument [Line Items]    
Number of trading days | day 20  
Number of consecutive trading days | day 30  
Threshold percentage of stock price trigger 130.00%  
Debt redemption price as percentage of principal amount 100.00%  
Private placement | Convertible debt | Convertible Senior Notes    
Debt Instrument [Line Items]    
Aggregate principal amount of debt $ 225,000,000.0  
Over-allotment option | Convertible debt | Convertible Senior Notes    
Debt Instrument [Line Items]    
Aggregate principal amount of debt $ 33,750,000  
Convertible, term one | Convertible debt | Convertible Senior Notes    
Debt Instrument [Line Items]    
Number of trading days | day 20  
Number of consecutive trading days | day 30  
Threshold percentage of stock price trigger 130.00%  
Convertible, term two | Convertible debt | Convertible Senior Notes    
Debt Instrument [Line Items]    
Number of trading days | day 5  
Number of consecutive trading days | day 5  
Threshold percentage of stock price trigger 98.00%