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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income from continuing operations									$ 232,982	$ 114,408	$ 187,774
Net income from discontinued operations, net of tax									0	12,392	0
Net income	$ 65,215	$ 79,900	$ 45,805	$ 42,062	$ 61,750	$ 51,450	$ 44,711	$ (31,111)	$ 232,982	$ 126,800	$ 187,774
Weighted-average shares used to calculate basic EPS									76,854	70,117	57,790
Effect of dilutive securities:
Employee equity awards									681	699	693
Weighted-average shares used to calculate diluted EPS									77,535	70,816	58,483
Basic EPS:
Basic EPS from continuing operations (in dollars per share)									$ 3.03	$ 1.63	$ 3.25
Basic EPS of discontinued operations (in dollars per share)									0.00	0.18	0.00
Basic EPS (in dollars per share)	$ 0.83	$ 1.02	$ 0.59	$ 0.58	$ 0.86	$ 0.73	$ 0.64	$ (0.46)	3.03	1.81	3.25
Diluted EPS:
Dilutive EPS from continuing operations (in dollars per share)									3.00	1.62	3.21
Dilutive EPS from discontinued operations (in dollars per share)									0.00	0.17	0.00
Diluted EPS (in dollars per share)	$ 0.82	$ 1.02	$ 0.58	$ 0.57	$ 0.86	$ 0.72	$ 0.64	$ (0.46)	$ 3.00	$ 1.79	$ 3.21