Earnings Per Share - Details of Basic and Diluted EPS (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 89,463	$ 109,750	$ 86,230	$ 89,336	$ 92,596	$ 84,280	$ 285,443	$ 266,212
Weighted average shares outstanding - basic	84,109			84,158			83,951	84,065
Dilutive effect of stock plans	1,624			1,885			1,619	1,995
Weighted average shares outstanding - diluted	85,733			86,043			85,570	86,060
Basic earnings per share	$ 1.06			$ 1.06			$ 3.40	$ 3.17
Diluted earnings per share	$ 1.04			$ 1.04			$ 3.34	$ 3.09
Anti-dilutive shares	25			0			8	0