Quarterly information (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 information (unaudited)
Net sales	$ 51,926	$ 60,554	$ 87,178	$ 67,029	$ 44,913	$ 41,671	$ 61,280	$ 52,298	$ 266,687	$ 200,162	$ 205,687
Gross profit	10,526	12,517	15,951	12,200	7,654	6,160	8,961	9,772	51,194	32,547	39,158
Selling, general, and administrative expenses	10,484	10,739	9,277	7,405	7,538	7,942	8,302	8,063	37,905	31,845	35,588
Operating income	42	1,778	6,674	4,795	116	(1,782)	659	1,709	13,289	$ 702	$ 3,570
Net income	$ (3,391)	$ 859	$ 6,070	$ 4,279	$ (1,177)	$ (2,512)	$ 598	$ (304)	$ (3,493)
Basic net income per common share	$ (0.25)	$ (0.02)							$ (0.26)
Diluted net income per common share	$ (0.25)	$ (0.02)							$ (0.26)
Basic weighted average shares	13,222,583,000	13,222,583,000							13,222,583
Diluted weighted average shares(	13,222,583,000	13,222,583,000							13,222,583