Quarterly Financial Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interim Period, Costs Not Allocable [Line Items]
Sales									$ 170,761	$ 160,088	$ 176,122
Operating expenses	$ 19,002	$ 19,294	$ 18,987	$ 20,542	$ 19,085	$ 19,299	$ 19,428	$ 20,874
Loss from operations	(1,877)	(920)	(1,187)	(3,180)	(1,125)	(1,801)	(1,368)	(4,470)	(7,164)	(8,764)	(1,322)
Net loss	$ (1,822)	$ (1,174)	$ (1,343)	$ (3,893)	$ (1,685)	$ (2,438)	$ (2,026)	$ (4,885)	$ (8,232)	$ (11,034)	$ (7,517)
Net (loss) income per share:
Basic (in dollars per share)	$ (0.11)	$ (0.07)	$ (0.08)	$ (0.23)	$ (0.10)	$ (0.15)	$ (0.12)	$ (0.30)		$ (0.67)	$ (0.47)
Diluted (in dollars per share)	$ (0.11)	$ (0.07)	$ (0.08)	$ (0.23)	$ (0.10)	$ (0.15)	$ (0.12)	$ (0.30)	$ (0.48)	$ (0.67)	$ (0.47)
Product
Interim Period, Costs Not Allocable [Line Items]
Sales	$ 16,756	$ 16,367	$ 16,162	$ 13,992	$ 13,613	$ 14,169	$ 14,323	$ 14,863
Cost of product and service sales	10,726	9,767	10,094	8,923	8,062	9,578	9,295	10,539
Service
Interim Period, Costs Not Allocable [Line Items]
Sales	26,995	27,150	27,230	26,109	25,365	26,281	26,126	25,348
Cost of product and service sales	$ 15,900	$ 15,376	$ 15,498	$ 13,816	$ 12,956	$ 13,374	$ 13,094	$ 13,268