Stockholders' Equity - Additional Information (Detail) - USD ($)			3 Months Ended			6 Months Ended
	May 02, 2018	Feb. 14, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Aug. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from public offering of common stock, net of issuance costs						$ 7,622,000	$ 2,126,341,000
Cash dividends declared (in dollars per share)	$ 2.28	$ 2.28	$ 2.28		$ 2.00	$ 4.56	$ 4.00
Payments of dividends			$ 181,800,000	$ 187,000,000		$ 368,759,000	$ 304,373,000
Restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividends payable			$ 2,800,000	$ 2,200,000		$ 2,800,000
Restricted stock units, approved (in shares)						546,375
Weighted-average grant date fair value (in dollars per share)						$ 379.83
Service period (in years)						3 years 6 months 21 days
At The Market (ATM) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock, equity offering agreement, authorized								$ 750,000,000.0
Issuance of common stock in public offering of common stock, shares						19,100
Issuance of common stock in public offering of common stock, net						$ 7,600,000
Proceeds from public offering of common stock, net of issuance costs						$ 363,300,000