Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 36,624	$ 22,638	$ 73,957	$ 52,684
Basic weighted average number of shares outstanding (shares)	196,270,119	195,747,954	196,243,714	195,746,817
Dilutive effect of stock options (shares)	2,171,196	1,961,128	2,080,292	2,000,830
Diluted weighted average number of shares outstanding (shares)	198,441,315	197,709,082	198,324,006	197,747,647
Basic net income per common share (in usd per share)	$ 0.19	$ 0.12	$ 0.38	$ 0.27
Diluted net income per common share (in usd per share)	$ 0.18	$ 0.11	$ 0.37	$ 0.27
Anti-dilutive shares excluded from diluted earnings per share computation (shares)	375,688	67,938	288,284	0