Details of Basic and Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 73,630	$ 69,557	$ 206,666	$ 195,653
Weighted average shares outstanding - basic	84,774	86,959	85,132	87,570
Dilutive effect of stock plans	1,814	1,717	1,770	1,785
Weighted average shares outstanding - diluted	86,588	88,676	86,902	89,355
Basic earnings per share	$ 0.87	$ 0.80	$ 2.43	$ 2.23
Diluted earnings per share	$ 0.85	$ 0.78	$ 2.38	$ 2.19
Anti-dilutive shares	27	269	112	242