Stockholders' Equity - Additional Information (Detail) - USD ($)												1 Months Ended				3 Months Ended								12 Months Ended
	Aug. 02, 2017	Apr. 26, 2017	Feb. 15, 2017	Nov. 02, 2016	Aug. 03, 2016	May 04, 2016	Feb. 18, 2016	Oct. 28, 2015	Jul. 29, 2015	May 07, 2015	Feb. 19, 2015	Mar. 31, 2017	Jun. 30, 2016	Nov. 30, 2015	Sep. 30, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2017	Jun. 15, 2016
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		2,994,792
Issuance of common stock in public offering of common stock, net												$ 2,126,300,000		$ 829,500,000
Underwriting discounts and commissions incurred in issuance of common stock in public offering of common stock												$ 58,700,000		32,300,000
Shares issued in exchange for convertible subordinated notes													380,779
Issuance of common stock and release of treasury stock for the exchanges and conversions of 4.75% convertible debt																									$ 150,025,000	$ 7,884,000
Adjustments to APIC, convertible debt with conversion feature													$ 141,700,000
Share price (dollars per share)																												$ 372.10
Common Stock, Dividends, Per Share, Cash Paid																$ 2	$ 2	$ 2	$ 2	$ 1.75	$ 1.75	$ 1.75	$ 1.75	$ 8	$ 7
Dividends declared per share (in dollars per share)	$ 2.00	$ 2	$ 2	$ 1.75	$ 1.75	$ 1.75	$ 1.75	$ 1.69	$ 1.69	$ 1.69	$ 1.69													$ 8	$ 7	$ 17.71
Dividends distributions																								$ 612,085,000	$ 492,403,000	$ 393,584,000
Short term dividend payable																$ 11,181,000				$ 11,999,000				11,181,000	11,999,000
Long term dividend payable																6,669,000				8,495,000				$ 6,669,000	8,495,000
Payments of Stock Issuance Costs														$ 700,000
At The Market (ATM)
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																								763,201
Issuance of common stock in public offering of common stock, net																								$ 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		390,625
Special Distribution
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Special distribution, amount															$ 627,000,000
Special distribution, per share (in dollars per share)															$ 10.95
Special distribution, payable date															Nov. 10, 2015
Closing price measurement period (in days)															3 days
Value of shares distributed per share (in dollars per share)															$ 297.03
Common stock shares issued															1,688,411
Common stock issued amount															$ 125,500,000
Record date															Oct. 08, 2015
Short term dividend payable																11,200,000				12,000,000				11,200,000	12,000,000
Long term dividend payable																$ 6,700,000				$ 8,500,000				$ 6,700,000	$ 8,500,000
2013 Share Repurchase Program | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury stock re-issued (shares)																								6,073		7,348
Treasury stock re-issued																								$ 2,600,000		$ 1,800,000
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%		4.75%		4.75%	4.75%	4.75%
Conversion of notes													$ 150,100,000
Conversion of notes, shares													1,981,662													101,947
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
4.75% convertible subordinated notes | 2013 Share Repurchase Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury stock re-issued (shares)																									7,099	11,784
Treasury stock re-issued																									$ 2,400,000	$ 3,500,000
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