Stockholders' Equity - Open Market Share Repurchases Activity (Detail) - USD ($)	1 Months Ended		3 Months Ended	12 Months Ended
	Mar. 31, 2017	Feb. 28, 2017	Mar. 31, 2017	Dec. 31, 2016	Jan. 31, 2017
Condensed Financial Statements Captions [Line Items]
Total Number of Shares Purchased, beginning balance			33,837,526
Number of Shares Purchased	365,228	564,623
Total Number of Shares Purchased, ending balance	34,767,377		34,767,377	33,837,526
Average price of common stock purchased	$ 45.15	$ 45.30	$ 46.14	$ 46.16
Dollar Value of Shares that may yet be Purchased under the Plans or Programs	$ 395,903,537	$ 412,392,848	$ 395,903,537	$ 437,970,016	$ 437,970,016
Publicly Announced Plans Or Programs
Condensed Financial Statements Captions [Line Items]
Total Number of Shares Purchased, beginning balance			33,837,526
Number of Shares Purchased	365,228	564,623
Total Number of Shares Purchased, ending balance	34,767,377		34,767,377	33,837,526