Consolidated Statements of Comprehensive Income - USD ($) $ 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
Statement Of Income And Comprehensive Income [Abstract]
Net income, Before tax amount	$ 3,482	$ 3,494	$ 3,231	$ 3,982	$ 3,012	$ 3,113	$ 2,800	$ 3,053	$ 14,189	$ 11,978	$ 10,803
Net unrealized holding (losses) gains on securities:
Unrealized holding (losses) gains arising during the period, Before tax amount									1,002	(4,192)	(1,419)
Reclassification adjustment for gains included in net income, Before tax amount									(1,500)	(674)	(783)
Unrealized holding (losses) gains arising during the period, Tax expense (benefit)									341	(1,426)	(483)
Reclassification adjustment for gains included in net income, Tax expense (benefit)									(510)	(229)	(266)
Unrealized holding (losses) gains arising during the period, Net of tax amount									661	(2,766)	(936)
Reclassification adjustment for gains included in net income, Net of tax amount									(990)	(445)	(517)
Other comprehensive loss, Before tax amount									(498)	(4,866)	(2,202)
Total comprehensive income, Before tax amount									13,691	7,112	8,601
Tax expense (benefit)	2,993	940	845	1,122	743	821	702	788	5,900	3,054	2,570
Other comprehensive loss, Tax expense (benefit)									(169)	(1,655)	(749)
Total comprehensive income, Tax expense (benefit)									5,731	1,399	1,821
Net income	$ 489	$ 2,554	$ 2,386	$ 2,860	$ 2,269	$ 2,292	$ 2,098	$ 2,265	8,289	8,924	8,233
Other comprehensive loss, Net of tax amount									(329)	(3,211)	(1,453)
Total comprehensive income, Net of tax amount									$ 7,960	$ 5,713	$ 6,780