Earnings Per Share - Computation of Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic earnings per share:
Net income	$ 290,124	$ 178,222
Weighted-average common shares outstanding (in shares)	434,174	430,600
Basic earnings per share (in dollars per share)	$ 0.67	$ 0.41
Diluted earnings per share:
Net income	$ 290,124	$ 178,222
Shares used in computation:
Weighted-average common shares outstanding (in shares)	434,174	430,600
Employee stock options (in shares)	16,185	14,858
Weighted-average number of shares (in shares)	450,359	445,458
Diluted earnings per share (in dollars per share)	$ 0.64	$ 0.40