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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic earnings per share:
Net income	$ 129,590	$ 51,517	$ 373,412	$ 119,930
Weighted-average common shares outstanding (in shares)	432,404	428,937	431,473	428,514
Basic earnings per share (in dollars per share)	$ 0.30	$ 0.12	$ 0.87	$ 0.28
Diluted earnings per share:
Net income	$ 129,590	$ 51,517	$ 373,412	$ 119,930
Shares used in computation:
Weighted-average common shares outstanding (in shares)	432,404	428,937	431,473	428,514
Employee stock options (in shares)	14,958	9,452	14,894	9,666
Weighted-average number of shares (in shares)	447,362	438,389	446,367	438,180
Diluted earnings per share (in dollars per share)	$ 0.29	$ 0.12	$ 0.84	$ 0.27