Earnings Per Share - Computation of Net Income Per Share (Details) - 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
Basic earnings per share:
Net income	$ 402,835	$ 129,590	$ 1,077,308	$ 373,412
Weighted-average common shares outstanding (in shares)	435,809	432,404	435,033	431,473
Basic earnings per share (in dollars per share)	$ 0.92	$ 0.30	$ 2.48	$ 0.87
Diluted earnings per share:
Net income	$ 402,835	$ 129,590	$ 1,077,308	$ 373,412
Shares used in computation:
Weighted-average common shares outstanding (in shares)	435,809	432,404	435,033	431,473
Employee stock options (in shares)	16,110	14,958	16,250	14,894
Weighted-average number of shares (in shares)	451,919	447,362	451,283	446,367
Diluted earnings per share (in dollars per share)	$ 0.89	$ 0.29	$ 2.39	$ 0.84