Earnings per Share (Detail) - Calculations Of Basic And Diluted Earnings Per Share - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income used for calculating basic and diluted earnings per common share	$ 36,433	$ 44,987
Denominator:
Weighted average number of common shares used in the calculation of basic earnings per share	82,835	82,451
Common stock equivalents associated with stock-based compensation plans (in shares)	1,260	1,013
Shares used in the calculation of diluted earnings per share	84,095	83,464
Basic earnings per share (in dollars per share)	$ 0.44	$ 0.55
Diluted earnings per share (in dollars per share)	$ 0.43	$ 0.54