Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Dec. 31, 2014	$ 8,688	$ 163,287	$ (5,672)	$ 166,303
Net income		15,833		15,833
Other comprehensive income (loss), net of tax			(2,265)	(2,265)
Cash dividend		(7,930)		(7,930)
Exercise of stock options	10	163		173
Balance at Dec. 31, 2015	8,698	171,353	(7,937)	172,114
Net income		14,942		14,942
Other comprehensive income (loss), net of tax			(722)	(722)
Cash dividend		(8,071)		(8,071)
Balance at Dec. 31, 2016	8,698	178,224	(8,659)	178,263
Net income		14,092		14,092
Other comprehensive income (loss), net of tax			682	682
Cash dividend		(8,141)		(8,141)
Reclassification of stranded tax effects from change in tax rate		1,718	(1,718)
Balance at Dec. 31, 2017	$ 8,698	$ 185,893	$ (9,695)	$ 184,896