Earnings Per Share - Computation of Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic earnings per share:
Net income	$ 65,600	$ 40,755	$ 243,822	$ 68,413
Weighted-average common shares outstanding (in shares)	431,396	428,483	431,000	428,300
Basic earnings per share (in dollars per share)	$ 0.15	$ 0.10	$ 0.57	$ 0.16
Diluted earnings per share:
Net income	$ 65,600	$ 40,755	$ 243,822	$ 68,413
Shares used in computation:
Weighted-average common shares outstanding (in shares)	431,396	428,483	431,000	428,300
Employee stock options (in shares)	14,866	9,671	14,862	9,773
Weighted-average number of shares (in shares)	446,262	438,154	445,862	438,073
Diluted earnings per share (in dollars per share)	$ 0.15	$ 0.09	$ 0.55	$ 0.16