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 available to common stockholders	$ 22,875	$ 25,120	$ 33,585	$ 36,540
Weighted average common shares outstanding, basic (in shares)	47,969,000	47,878,000	47,949,000	47,861,000
Dilutive SARs (treasury method) (in shares)		9,000	3,000	16,000
Weighed average common shares outstanding, dilutive (in shares)	47,969,000	47,887,000	47,952,000	47,877,000
Earnings per share - basic (in dollars per share)	$ 0.48	$ 0.52	$ 0.70	$ 0.76
Earnings per share - diluted (in dollars per share)	$ 0.48	$ 0.52	$ 0.70	$ 0.76
Net Income Per Share Calculations
Dilutive SARs (treasury method) (in shares)		9,000	3,000	16,000
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