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Convertible Senior Notes - Additional Information (Detail)
 1 Months Ended 3 Months Ended 12 Months Ended
Jul. 22, 2019
USD ($)
shares
Jul. 19, 2019
USD ($)
$ / shares
Sep. 23, 2019
USD ($)
shares
Dec. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
Day
Dec. 31, 2019
USD ($)
Jul. 16, 2019
USD ($)
Debt Instrument [Line Items]              
Proceeds from issuance of convertible senior notes, net of costs           $ 278,466,000  
Notes threshold percentage of stock price trigger       130.00%      
Notes threshold trading days | Day         20    
Debt instrument amount convertible into equity       $ 3,000 $ 3,000    
Notes threshold consecutive trading days | Day         30    
Total consideration on conversion           198,757,000  
Loss on extinguishment of debt           $ 5,650,000  
0.375% Convertible Senior Notes due 2024              
Debt Instrument [Line Items]              
Notes issued   $ 287,500,000          
Notes, interest rate   0.375%   0.375% 0.375%    
Proceeds from issuance of convertible senior notes, net of costs   $ 278,500,000          
Interest repayment terms   Interest is payable semi-annually in arrears on January 15 and July 15 of each year, beginning on January 15, 2020.          
Notes, due date   Jul. 15, 2024          
Notes conversion ratio per $1,000 principal amount   8.6749          
Notes initial conversion price | $ / shares   $ 115.28          
Notes redemption price   100.00%          
Contractual coupon interest         $ 1,100,000    
Accretion of the debt discount         9,600,000    
Amortization of the debt issuance costs         $ 1,400,000    
Effective interest rate on the Notes       5.10% 5.10%    
Notes, carrying value       $ 243,700,000 $ 243,700,000    
Fair value of the note       501,000,000.0 501,000,000.0    
Additional Notes issued   $ 37,500,000          
Discount rate           4.50%  
Proceeds allocated to the conversion feature           $ 52,100,000  
Transaction costs attributable to liability component         7,400,000    
Transaction costs attributable to equity component       $ 1,600,000 $ 1,600,000    
2.125% Convertible Senior Notes due 2021              
Debt Instrument [Line Items]              
Notes issued             $ 92,000,000.0
Notes, interest rate       2.125% 2.125%    
Contractual coupon interest         $ 1,300,000    
Accretion of the debt discount         2,400,000    
Amortization of the debt issuance costs         $ 400,000    
Effective interest rate on the Notes       6.60% 6.60%    
Repayment Of Senior Debt   92,300,000 $ 23,000,000.0        
Accrued interest   $ 300,000          
Total consideration on conversion $ 253,300,000            
Face amount of remaining convertible debt     60,800,000        
Equity component of converted debt $ 163,600,000   38,300,000        
Loss on extinguishment of debt     $ 1,100,000     $ 4,600,000  
2.125% Convertible Senior Notes due 2021 | Common Stock [Member]              
Debt Instrument [Line Items]              
Conversion of Convertible Securities Stock Issued | shares | shares 1,850,155   466,045        
Conversion of Convertible Securities Stock Issued | value $ 161,000,000.0   $ 37,800,000