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 available to common stockholders	$ 11,508	$ 9,845	$ 10,710	$ 11,420
Weighted average common shares outstanding, basic (in shares)	47,972,000	47,880,000	47,938,000	47,853,000
Dilutive SARs (treasury method) (in shares)	0	12,000	5,000	20,000
Weighed average common shares outstanding, dilutive (in shares)	47,972,000	47,892,000	47,943,000	47,873,000
Earnings per share - basic (in dollars per share)	$ 0.24	$ 0.21	$ 0.22	$ 0.24
Earnings per share - diluted (in dollars per share)	$ 0.24	$ 0.21	$ 0.22	$ 0.24
Net Income Per Share Calculations
Dilutive SARs (treasury method) (in shares)	0	12,000	5,000	20,000
Stock Appreciation Rights (SARs)
Earnings Per Share [Abstract]
Dilutive SARs (treasury method) (in shares)			0	65,436
Net Income Per Share Calculations
Dilutive SARs (treasury method) (in shares)			0	65,436