Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic earnings per share:
Net income	$ 270,650	$ 384,349	$ 614,702	$ 674,473
Weighted-average common shares outstanding (in shares)	437,587	435,097	437,271	434,638
Basic earnings per share (in dollars per share)	$ 0.62	$ 0.88	$ 1.41	$ 1.55
Diluted earnings per share:
Net income	$ 270,650	$ 384,349	$ 614,702	$ 674,473
Shares used in computation:
Weighted-average common shares outstanding (in shares)	437,587	435,097	437,271	434,638
Employee stock options (in shares)	14,608	16,455	14,792	16,320
Weighted-average number of shares (in shares)	452,195	451,552	452,063	450,958
Diluted earnings per share (in dollars per share)	$ 0.60	$ 0.85	$ 1.36	$ 1.50