Earnings Per Common Share (Calculations of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Distributed earnings allocated to common shareholders									$ 27,082	$ 26,503	$ 21,334
Undistributed earnings allocated to common shareholders									7,313	26,796	24,660
Net earnings allocated to common shareholders									$ 34,395	$ 53,299	$ 45,994
Weighted-average number of common shares outstanding – basic	19,302,919	19,504,503	19,720,315	20,367,564	20,407,505	20,415,245	20,277,028	19,366,008	19,721,772	20,120,119	18,991,768
Effect of potentially dilutive common shares									122,034	153,606	130,492
Total weighted-average diluted common shares outstanding	19,442,284	19,637,689	19,858,880	20,538,214	20,599,127	20,595,769	20,442,366	19,508,868	19,843,806	20,273,725	19,122,260
Earnings per common share – basic	$ 1.06	$ 0.52	$ 0.24	$ (0.04)	$ 0.72	$ 0.72	$ 0.47	$ 0.74	$ 1.74	$ 2.65	$ 2.42
Earnings per common share – diluted	1.05	0.51	0.23	(0.04)	0.72	0.72	0.46	0.73	$ 1.73	$ 2.63	$ 2.41
Antidilutive Securities Excluded from Computation of Earnings Per Share
Restricted shares, stock options and stock appreciation rights									64,145	0	1,748
Earnings per common share – basic	$ 1.06	$ 0.52	$ 0.24	$ (0.04)	$ 0.72	$ 0.72	$ 0.47	$ 0.74	$ 1.74	$ 2.65	$ 2.42
Distributed earnings allocated to common shareholders									$ 27,082	$ 26,503	$ 21,334
Undistributed Earnings, Diluted									7,313	26,796	24,660
Net earnings allocated to common shareholders									$ 34,395	$ 53,299	$ 45,994
Weighted-average number of common shares outstanding – basic	19,302,919	19,504,503	19,720,315	20,367,564	20,407,505	20,415,245	20,277,028	19,366,008	19,721,772	20,120,119	18,991,768
Effect of potentially dilutive common shares									122,034	153,606	130,492
Weighted-average number of common shares outstanding – diluted	19,442,284	19,637,689	19,858,880	20,538,214	20,599,127	20,595,769	20,442,366	19,508,868	19,843,806	20,273,725	19,122,260
Earnings per common share – diluted	$ 1.05	$ 0.51	$ 0.23	$ (0.04)	$ 0.72	$ 0.72	$ 0.46	$ 0.73	$ 1.73	$ 2.63	$ 2.41