Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 22,638	$ 21,911	$ 52,684	$ 53,064
Basic weighted average number of shares outstanding	195,747,954	195,733,692	195,746,817	195,727,329
Dilutive effect of stock options	1,961,128	2,094,141	2,000,830	2,063,191
Diluted weighted average number of shares outstanding	197,709,082	197,827,833	197,747,647	197,790,520
Basic net income per common share (in usd per share)	$ 0.12	$ 0.11	$ 0.27	$ 0.27
Diluted net income per common share (in usd per share)	$ 0.11	$ 0.11	$ 0.27	$ 0.27
Anti-dilutive shares excluded from diluted earnings per share computation	67,938	0	0	0