Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income from continuing operations									$ 365,359	$ 232,982	$ 114,408
Net income from discontinued operations, net of tax									0	0	12,392
Net income	$ 110,022	$ 124,825	$ 67,618	$ 62,894	$ 65,215	$ 79,900	$ 45,805	$ 42,062	$ 365,359	$ 232,982	$ 126,800
Weighted-average shares used to calculate basic EPS									79,779	76,854	70,117
Effect of dilutive securities:
Employee equity awards									418	681	699
Weighted-average shares used to calculate diluted EPS									80,197	77,535	70,816
Basic EPS:
Basic EPS from continuing operations (in dollars per share)									$ 4.58	$ 3.03	$ 1.63
Basic EPS of discontinued operations (in dollars per share)									0.00	0.00	0.18
Basic EPS (in dollars per share)	$ 1.37	$ 1.56	$ 0.85	$ 0.79	$ 0.83	$ 1.02	$ 0.59	$ 0.58	4.58	3.03	1.81
Diluted EPS:
Dilutive EPS from continuing operations (in dollars per share)									4.56	3.00	1.62
Dilutive EPS from discontinued operations (in dollars per share)									0.00	0.00	0.17
Diluted EPS (in dollars per share)	$ 1.36	$ 1.55	$ 0.85	$ 0.79	$ 0.82	$ 1.02	$ 0.58	$ 0.57	$ 4.56	$ 3.00	$ 1.79