Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest Income	$ 28,610	$ 27,986	$ 27,401	$ 27,033	$ 27,101	$ 26,734	$ 26,850	$ 22,680	$ 111,030		$ 103,365		$ 81,620
Net Interest Income	25,454	24,917	24,813	24,725	24,889	24,560	24,671	20,784	99,909		94,904		75,552
Net Income	$ 11,621	$ 9,660	$ 9,839	$ 9,556	$ 10,065	$ 10,185	$ 9,788	$ 5,146	$ 40,676		$ 35,184		$ 30,064
Basic Earnings per Share (in USD per share)	$ 0.51	$ 0.42	$ 0.43	$ 0.42	$ 0.44	$ 0.45	$ 0.43	$ 0.25	$ 1.77	[1],[2]	$ 1.57	[1],[2]	$ 1.51	[1],[2]
Diluted Earnings per Share (in USD per share)	$ 0.51	$ 0.42	$ 0.43	$ 0.42	$ 0.44	$ 0.45	$ 0.43	$ 0.25	$ 1.77	[1],[2]	$ 1.57	[1],[2]	$ 1.51	[1],[2]

[1] Per share data has been adjusted to reflect a 3-for-2 stock split on April 21, 2017.

[2] Share and per share data has been adjusted to reflect a 3-for-2 stock split on April 21, 2017.