Earnings Per Share - Computation of Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Basic earnings per share:
Net income	$ 27,658	$ 23,696
Weighted-average common shares outstanding (in shares)	428,117	423,624
Basic earnings per share (in dollars per share)	$ 0.06	$ 0.06
Diluted earnings per share:
Net income	$ 27,658	$ 23,696
Shares used in computation:
Weighted-average common shares outstanding (in shares)	428,117	423,624
Employee stock options (in shares)	9,876	10,185
Weighted-average number of shares (in shares)	437,993	433,809
Diluted earnings per share (in dollars per share)	$ 0.06	$ 0.05