Segment Information - Financial Data by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Sales to external customers	$ 40,220	$ 39,751	$ 71,590	$ 71,460
Operating income	3,768	3,625	5,303	4,990
Interest expense, net	491	445	994	850
Other income, net	14	74	12	61
Consolidated income before income taxes	3,263	3,106	4,297	4,079
Assets	117,030		117,030		$ 109,478
United States
Sales to external customers	34,958	34,778	62,423	62,555
Operating income	3,271	2,912	4,529	4,028
Assets	105,556		105,556		99,721
Canada
Sales to external customers	2,216	2,472	3,628	4,024
Operating income	360	543	495	682
Assets	4,880		4,880		3,839
Europe
Sales to external customers	3,046	2,501	5,539	4,881
Operating income	137	$ 170	279	$ 280
Assets	$ 6,594		$ 6,594		$ 5,918