Stockholders' Equity (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2014	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of common stock (shares)					1,962,989	0
Aggregate cost of stock repurchased					$ 91,165
Aggregate cost of stock repurchased					$ 91,165
Shares of treasury stock					1,050,820
Treasury stock, shares outstanding			1,050,820		1,050,820
Cash dividend per share	$ 0.13	$ 0.115	$ 0.13	$ 0.115	$ 0.39	$ 0.345
Cash dividend per common share, increase	$ 0.015
Cash dividends on common stock					$ 48,246	$ 42,770
Repurchase of common stock, maximum value			$ 1,200,000		1,200,000
Remaining value of common stock authorized under repurchase program			$ 317,479		$ 317,479
Treasury Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of treasury stock					1,050,820
Treasury stock, shares outstanding			1,050,820		1,050,820
Treasury stock at cost					$ 49,458
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of award					$ 46.43
Vested deferred RSUs outstanding		223,752	256,621	223,752	256,621	223,752
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value of award					$ 46.47
Performance period end date					Dec. 31, 2017
Performance Shares [Member] | Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of award					3 years
Performance Shares [Member] | Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of award					4 years