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Convertible Senior Notes - Additional Information (Detail)
$ / shares in Units, shares in Millions
9 Months Ended
May 02, 2017
USD ($)
d
$ / shares
shares
Sep. 30, 2020
USD ($)
shares
Dec. 31, 2019
USD ($)
Debt Instrument [Line Items]      
Principal amount   $ 517,500,000 $ 517,500,000
2.25% Convertible Senior Notes due 2024      
Debt Instrument [Line Items]      
Principal amount $ 517,500,000    
Interest rate percentage 2.25%    
Proceeds from issuance $ 502,800,000    
Threshold common stock trading days | d 20    
Threshold consecutive common stock trading days | d 30    
Threshold percentage of common stock price trigger 130.00%    
Number of consecutive business days 5 days    
Principal amount on conversion rate $ 1,000    
Minimum percentage of common stock price trigger 98.00%    
Conversion observation period 25 days    
Convertible senior notes convertible in to shares 0.0131711    
Convertible senior notes conversion price (in USD per share) | $ / shares $ 75.92    
Shares issued to settle notes at initial conversion rate (in shares) | shares 6.8 6.8  
Convertible senior note premium 42.50%    
Market price of common stock (in USD per share) | $ / shares $ 53.28    
Convertible senior notes redemption rate 100.00%    
Convertible senior note carrying value of the liability component $ 368,300,000    
Convertible senior note assumed borrowing rate 7.50%    
Convertible senior note carrying value of the equity component $ 149,200,000    
Convertible senior notes term 7 years    
Discount on liability component, remaining amortization period   3 years 7 months 6 days  
Transaction cost related to issuance of convertible senior notes $ 14,700,000    
Debt instrument events of default percentage of principal and accrued and unpaid interest due and payable upon default 100.00%    
Convertible senior notes fair value   $ 713,000,000.0 $ 596,800,000