Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity [Abstract]
Repurchase and retirement of common stock			$ 247,795
Repurchase and retirement of common stock (shares)			1,752
Shares remaining available for repurchases (shares)	3,298		3,298
Cash dividend paid during period, per share (in dollars per share)	$ 0.53	$ 0.48	$ 1.59	$ 1.44
Dividends declared (in dollars per share)	$ 0.53
Common stock excluded from calculation of diluted earnings per share (shares)	1,087	647	971	562