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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic earnings per share:
Net income	$ 384,349	$ 65,600	$ 674,473	$ 243,822
Weighted-average common shares outstanding (in shares)	435,097	431,396	434,638	431,000
Basic earnings per share (in dollars per share)	$ 0.88	$ 0.15	$ 1.55	$ 0.57
Diluted earnings per share:
Net income	$ 384,349	$ 65,600	$ 674,473	$ 243,822
Shares used in computation:
Weighted-average common shares outstanding (in shares)	435,097	431,396	434,638	431,000
Employee stock options (in shares)	16,455	14,866	16,320	14,862
Weighted-average number of shares (in shares)	451,552	446,262	450,958	445,862
Diluted earnings per share (in dollars per share)	$ 0.85	$ 0.15	$ 1.50	$ 0.55