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Convertible Senior Notes - Additional Information (Detail)
 1 Months Ended 3 Months Ended 6 Months Ended
Jul. 22, 2019
USD ($)
shares
Jul. 19, 2019
USD ($)
$ / shares
Sep. 23, 2019
USD ($)
shares
Jun. 30, 2020
USD ($)
shares
Jun. 30, 2019
USD ($)
Jun. 30, 2020
USD ($)
Jun. 30, 2019
USD ($)
Jul. 31, 2019
USD ($)
Jul. 16, 2019
USD ($)
Debt Instrument [Line Items]                  
Accretion of the debt discount           $ 5,415,000 $ 2,231,000    
Loss on extinguishment of debt           (5,700,000)      
Common Stock [Member]                  
Debt Instrument [Line Items]                  
Conversion of Convertible Securities Stock Issued | shares | shares       2,316,200          
0.375% Convertible Senior Notes due 2024                  
Debt Instrument [Line Items]                  
Notes issued   $ 287,500,000           $ 287,500,000  
Notes, interest rate   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       $ 300,000   500,000      
Accretion of the debt discount       2,400,000   4,700,000      
Amortization of the debt issuance costs       $ 300,000   $ 700,000      
Effective interest rate on the Notes       5.10%   5.10%      
Notes, carrying value       $ 238,200,000   $ 238,200,000      
Fair value of the note       364,000,000.0   $ 364,000,000.0      
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       115,000,000.0   $ 115,000,000.0     $ 92,000,000.0
Notes, interest rate                 2.125%
Notes, due date   Jun. 01, 2021       Jun. 01, 2021      
Notes redemption price     100.00%            
Notes issued, fair value       $ 96,300,000   $ 96,300,000      
Contractual coupon interest         $ 600,000   1,200,000    
Accretion of the debt discount         1,000,000.0   1,900,000    
Amortization of the debt issuance costs         200,000   300,000    
Effective interest rate on the Notes       6.60%   6.60%      
Notes, carrying value         105,700,000   105,700,000    
Fair value of the note         $ 310,500,000   $ 310,500,000    
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            
2.125% Non Convertible Senior Notes due 2021                  
Debt Instrument [Line Items]                  
Effective interest rate on the Notes       3.90%   3.90%      
Equity component of converted debt       $ 200,100,000   $ 200,100,000