Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity [Abstract]
Repurchase and retirement of common stock			$ 65,622
Repurchase and retirement of common stock (shares)			758
Shares remaining available for repurchases (shares)	6,705		6,705
Cash dividend paid during period, per share (in dollars per share)	$ 0.58	$ 0.55	$ 1.16	$ 1.1
Common stock excluded from calculation of diluted earnings per share (shares)	3,626	1,809	3,398	1,672