Earnings per Share (Detail) - Calculations Of Basic And Diluted Earnings Per Share - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income used for calculating basic and diluted earnings per common share	$ 30,484	$ 51,626	$ 44,987	$ 30,366	$ 96,614	$ 127,097	$ 109,872
Denominator:
Weighted average number of common shares used in the calculation of basic earnings per share	82,638			82,989		82,549	84,244
Common stock equivalents associated with stock-based compensation plans (in shares)	1,165			1,124		1,212	1,191
Shares used in the calculation of diluted earnings per share	83,803			84,113		83,761	85,435
Basic earnings per share (in dollars per share)	$ 0.37	$ 0.63	$ 0.55	$ 0.37	$ 1.17	$ 1.54	$ 1.30
Diluted earnings per share (in dollars per share)	$ 0.36	$ 0.62	$ 0.54	$ 0.36	$ 1.15	$ 1.52	$ 1.29