Stockholders' Equity - Open Market Share Repurchases Activity (Detail) - USD ($)	1 Months Ended											12 Months Ended
	Nov. 30, 2016	Oct. 31, 2016	Sep. 30, 2016	Aug. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Feb. 28, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements Captions [Line Items]
Total Number of Shares Purchased, beginning balance											25,762,411	25,762,411
Number of Shares Purchased	326,679	139,937	183,968	224,800	1,286,936	1,478,685	1,320,614	1,368,352	429,617	687,473	628,054
Total Number of Shares Purchased, ending balance												33,837,526	25,762,411
Average price of common stock purchased	$ 46.17	$ 51.73	$ 53.01	$ 53.61	$ 53.66	$ 53.84	$ 52.23	$ 52.91	$ 51.48	$ 47.41	$ 45.62	$ 46.16	$ 44.43
Dollar Value of Shares that may yet be Purchased under the Plans or Programs	$ 437,970,016	$ 453,051,573	$ 460,290,434	$ 470,042,455	$ 482,094,449	$ 551,145,264	$ 630,761,673	$ 699,730,694	$ 772,128,085	$ 794,246,197	$ 826,841,315	$ 437,970,016	$ 855,495,985
Publicly Announced Plans Or Programs
Condensed Financial Statements Captions [Line Items]
Total Number of Shares Purchased, beginning balance											25,762,411	25,762,411
Number of Shares Purchased	326,679	139,937	183,968	224,800	1,286,936	1,478,685	1,320,614	1,368,352	429,617	687,473	628,054
Total Number of Shares Purchased, ending balance												33,837,526	25,762,411