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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic earnings per share:
Net income	$ 51,517	$ 29,432	$ 119,930	$ 79,463
Weighted-average common shares outstanding (in shares)	428,937	426,869	428,514	425,289
Basic earnings per share (in dollars per share)	$ 0.12	$ 0.07	$ 0.28	$ 0.19
Diluted earnings per share:
Net income	$ 51,517	$ 29,432	$ 119,930	$ 79,463
Shares used in computation:
Weighted-average common shares outstanding (in shares)	428,937	426,869	428,514	425,289
Employee stock options (in shares)	9,452	10,737	9,666	10,560
Weighted-average number of shares (in shares)	438,389	437,606	438,180	435,849
Diluted earnings per share (in dollars per share)	$ 0.12	$ 0.07	$ 0.27	$ 0.18