Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income		$ 25,405	$ 21,946	$ 46,664	$ 46,307
Earnings allocated to participating securities - preferred shares		45	39	82	82
Earnings allocated to participating securities - nonvested restricted shares		343	248	578	475
Earnings allocated to common shareholders, Basic		$ 25,017	$ 21,659	$ 46,004	$ 45,750
Weighted average common shares outstanding		57,185	57,055	57,149	56,999
Basic earnings per common share		$ 0.44	$ 0.38	$ 0.80	$ 0.80
Earnings allocated to common shareholders, Diluted	[1]	$ 25,017	$ 21,659	$ 46,004	$ 45,750
Dilutive effect of equity awards and warrants		10	14	11	13
Weighted average diluted common shares outstanding		57,195	57,069	57,160	57,012
Diluted earnings per common share		$ 0.44	$ 0.38	$ 0.80	$ 0.80
Potentially dilutive share options that were not included in the computation of diluted EPS because to do so would be anti-dilutive.		19	37	23	45

[1] Earnings allocated to common shareholders for basic and diluted EPS may differ under the two-class method as a result of adding common stock equivalents for options and warrants to dilutive shares outstanding, which alters the ratio used to allocate earnings to common shareholders and participating securities for the purposes of calculating diluted EPS.