Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 124,825	$ 79,900	$ 255,337	$ 167,767
Weighted-average shares used to calculate basic EPS (in shares)	79,872	78,055	79,533	76,283
Effect of dilutive securities:
Employee equity awards (in shares)	411	664	423	665
Weighted-average shares used to calculate diluted EPS (in shares)	80,283	78,719	79,956	76,948
Basic EPS (in dollars per share)	$ 1.56	$ 1.02	$ 3.21	$ 2.20
Diluted EPS (in dollars per share)	$ 1.55	$ 1.02	$ 3.19	$ 2.18