Condensed Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Sales	$ 89,096	$ 87,956
Cost of sales	72,436	69,005
Gross profit	16,660	18,951
Selling, general and administrative expenses	8,147	8,562
Operating income	8,513	10,389
Interest expense, net	(252)	(207)
Income before income taxes	8,261	10,182
Income tax expense (benefit)	(1,459)	1,255
Net income	9,720	8,927
Income attributable to participating securities	66	175
Net income attributable to common shareholders and used in earnings per share calculation (Note 5)	$ 9,654	$ 8,752
Share information:
Basic and diluted weighted average common shares (in shares)	16,967,631	16,843,255
Basic and diluted earnings per common share (in dollars per share)	$ 0.57	$ 0.52