Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended			6 Months Ended
	Apr. 26, 2017	Feb. 15, 2017	Mar. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued and sold (in shares)			6,069,444
Stock issued, new issues			$ 2,126,300
Proceeds from issuance of stock			57,900
Payments of stock issuance costs			800
Quarterly cash dividend declared (in dollars per share)	$ 2.00	$ 2.00		$ 2		$ 1.75	$ 4	$ 3.5
Payments of dividends				$ 156,300	$ 148,100		$ 304,373	$ 246,694
Restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in period							511,548
Weighted-average grant date fair value of shares issued (in dollars per share)							$ 367.23
Weighted average requisite service period of shares issued							3 years 5 months 24 days
Special Distribution [Member] | Restricted stock units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividends payable			$ 2,600	$ 2,700	$ 2,600		$ 2,700
Over-Allotment Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued and sold (in shares)			791,666