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Stockholders' Equity - Narrative (Detail) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
May 31, 2020
Mar. 31, 2019
Mar. 31, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Issuance of common stock in public offering of common stock (in shares) 2,587,500 2,985,575          
Issuance of common stock in public offering of common stock $ 1,683,100,000 $ 1,213,400,000          
Restricted stock units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Restricted stock units, approved (in shares)         680,543    
Weighted-average grant date fair value (in dollars per share)         $ 583.99    
Service period (in years)         3 years 3 months 29 days    
ATM Program              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Issuance of common stock in public offering of common stock (in shares)         162,530 722,361  
Issuance of common stock in public offering of common stock     $ 101,791,000 $ 348,121,000 $ 101,800,000 $ 348,200,000  
Sale of stock, equity offering agreement, authorized             $ 750,000,000.0