Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended									12 Months Ended
	Mar. 31, 2017	Jun. 30, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized			300,000,000				300,000,000					300,000,000	300,000,000
Preferred stock, shares authorized			100,000,000				100,000,000					100,000,000	100,000,000
Preferred stock, shares issued			0				0					0	0
Preferred stock, shares outstanding			0				0					0	0
Issuance of common stock in public offering of common stock, shares	6,069,444
Issuance of common stock in public offering of common stock, net	$ 2,126,300,000
Underwriting discounts and commissions incurred in issuance of common stock in public offering of common stock	$ 58,700,000
Dividends per share (in dollars per share)			$ 2.28	$ 2.28	$ 2.28	$ 2.28	$ 2	$ 2	$ 2	$ 2	$ 1.75	$ 9.12	$ 8
Dividends distributions												$ 727,448,000	$ 612,085,000	$ 492,403,000
Short term dividend payable			$ 8,795,000				$ 11,181,000					8,795,000	11,181,000
Long term dividend payable			6,545,000				6,669,000					6,545,000	$ 6,669,000
2018 ATM Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock, equity offering agreement, authorized			750,000,000.0									$ 750,000,000.0
2017 ATM Program
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												930,934	763,201
Issuance of common stock in public offering of common stock, net												$ 388,172,000	$ 355,082,000
Over-Allotment Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock in public offering of common stock, shares	791,666
Special Distribution
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Short term dividend payable			8,800,000				11,200,000					8,800,000	11,200,000
Long term dividend payable			$ 6,500,000				$ 6,700,000					$ 6,500,000	$ 6,700,000
4.75% convertible subordinated notes
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Interest rate (percent)		4.75%	4.75%									4.75%
Conversion of notes		$ 150,100,000
Conversion of notes, shares		1,981,662
Shares of common stock received, capped call, shares		380,779
Value of common stock received, capped call		$ 141,700,000
Average price of common stock shares repurchased (in dollars per share)		$ 372.10
Series A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized			25,000,000									25,000,000
Series A-1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized			25,000,000									25,000,000
Undesignated
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares authorized			50,000,000									50,000,000