Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 21,482	$ 27,066	$ 95,439	$ 79,750
Basic weighted average number of shares outstanding (shares)	196,445,684	196,062,348	196,311,529	195,852,404
Dilutive effect of stock options (shares)	3,006,624	2,192,460	2,978,488	2,176,139
Diluted weighted average number of shares outstanding (shares)	199,452,308	198,254,808	199,290,017	198,028,543
Basic net income per common share (in usd per share)	$ 0.11	$ 0.14	$ 0.49	$ 0.41
Diluted net income per common share (in usd per share)	$ 0.11	$ 0.14	$ 0.48	$ 0.40
Anti-dilutive shares excluded from diluted earnings per share computation (shares)	385,861	86,733	407,845	29,229