Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 4,350	$ 4,871	$ 4,378
Securities available for sale:
Unrealized holding gains (losses) on available-for-sale securities	2,153	(3,719)	(692)
Tax effect	(733)	1,265	235
Reclassification adjustment for net gains realized in net income	(7)	(466)	(75)
Tax effect	3	158	26
Total securities available-for-sale	1,416	(2,762)	(506)
Change in post-retirement obligations	14	39	(108)
Total other comprehensive income (loss)	1,430	(2,723)	(614)
Total comprehensive income	$ 5,780	$ 2,148	$ 3,764