Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Equity [Abstract]
Repurchase and retirement of common stock			$ 157,739
Repurchase and retirement of common stock (shares)			1,072
Shares remaining available for repurchases (shares)	3,978		3,978
Cash dividend paid during period, per share (in dollars per share)	$ 0.53	$ 0.48	$ 1.06	$ 0.96
Dividends declared (in dollars per share)	$ 0.53
Common stock excluded from calculation of diluted earnings per share (shares)	1,080	665	912	513