Stockholders' Equity - Narrative (Detail) - USD ($)	1 Months Ended		3 Months Ended				9 Months Ended
	May 31, 2020	Mar. 31, 2019	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 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)							709,450
Weighted-average grant date fair value (in dollars per share)							$ 593.74
Service period (in years)							3 years 3 months 18 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)			252,982		181,194		415,512	903,555
Issuance of common stock in public offering of common stock			$ 196,477,000	$ 101,791,000	$ 99,400,000	$ 348,121,000	$ 298,300,000	$ 447,500,000
Sale of stock, equity offering agreement, authorized									$ 750,000,000.0