Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income		$ 27,484	$ 25,780	$ 74,148	$ 72,087
Earnings allocated to participating securities - preferred shares		48	45	131	127
Earnings allocated to participating securities - nonvested restricted shares		378	296	953	772
Earnings allocated to common shareholders, Basic		$ 27,058	$ 25,439	$ 73,064	$ 71,188
Weighted average common shares outstanding		57,215	57,051	57,173	57,007
Basic earnings per common share		$ 0.47	$ 0.45	$ 1.28	$ 1.25
Earnings allocated to common shareholders, Diluted	[1]	$ 27,058	$ 25,439	$ 73,064	$ 71,188
Dilutive effect of equity awards and warrants		10	13	10	14
Weighted average diluted common shares outstanding		57,225	57,064	57,183	57,021
Diluted earnings per common share		$ 0.47	$ 0.45	$ 1.28	$ 1.25
Potentially dilutive share options that were not included in the computation of diluted EPS because to do so would be anti-dilutive.		15	29	20	40

[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.