Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Equity [Abstract]
Repurchase and retirement of common stock			$ 143,876
Repurchase and retirement of common stock (shares)			1,692
Shares remaining available for repurchases (shares)	8,679		8,679
Cash dividend paid during period, per share (in dollars per share)	$ 0.55	$ 0.53	$ 1.1	$ 1.06
Dividends declared (in dollars per share)	$ 0.55
Common stock excluded from calculation of diluted earnings per share (shares)	1,809	1,080