Segment Information - Financial Data by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Sales to external customers	$ 39,751	$ 38,849	$ 71,460	$ 66,595
Operating income	3,625	3,911	4,990	5,125
Interest expense, net	445	321	850	583
Other (income) expense, net	74	(29)	61	(16)
Consolidated income before income taxes	3,106	3,619	4,079	4,558
Assets	118,578		118,578		$ 114,730
United States
Sales to external customers	34,778	34,140	62,555	58,615
Operating income	2,912	3,289	4,028	4,419
Assets	107,841		107,841		104,431
Canada
Sales to external customers	2,472	2,503	4,024	3,895
Operating income	543	503	682	535
Assets	4,758		4,758		4,926
Europe
Sales to external customers	2,501	2,206	4,881	4,085
Operating income	170	$ 119	280	$ 171
Assets	$ 5,979		$ 5,979		$ 5,373