Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income Available to Common Shareholders	$ 10,713	$ 20,692	$ 20,979	$ 17,616	$ 9,669	$ 13,932	$ 14,685	$ 16,026	$ 70,002	$ 54,310	$ 52,128
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									654	591	623
Distributed earnings allocated to common shares outstanding									32,483	27,497	25,710
Undistributed earnings allocated to common shares outstanding									36,865	26,222	25,795
Net earnings allocated to common shareholders	$ 10,623	$ 20,491	$ 20,768	$ 17,421	$ 9,560	$ 13,778	$ 14,531	$ 15,849	$ 69,348	$ 53,719	$ 51,505
Average shares outstanding, basic	15,603,000	15,340,000	15,326,000	15,414,000	15,472,000	15,485,000	15,462,000	15,252,000	15,421,000	15,412,000	14,900,000
Effect of dilutive securities									18,000	24,000	13,000
Average shares outstanding, diluted	15,618,000	15,358,000	15,345,000	15,436,000	15,497,000	15,505,000	15,487,000	15,277,000	15,439,000	15,436,000	14,913,000
Basic earnings per share	$ 0.68	$ 1.34	$ 1.36	$ 1.13	$ 0.62	$ 0.89	$ 0.94	$ 1.04	$ 4.50	$ 3.49	$ 3.46
Diluted earnings per share	$ 0.68	$ 1.33	$ 1.35	$ 1.13	$ 0.62	$ 0.89	$ 0.94	$ 1.04	$ 4.49	$ 3.48	$ 3.45
Options to purchase shares of common stock, anti-dilutive									328	2,785	2,096