SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - A/R, Inventories, and Other Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018		Dec. 31, 2017
Accounts Receivable and Allowance for Doubtful Accounts
Accounts Receivable Allowances	$ 246		$ 222		$ 222
Inventories
Raw Materials	16,197		16,769
Work in Process	698		1,015
Finished Goods	252		332
Reserves	(1,163)		(1,112)
Total	15,984		17,004	[1]
Finite-Lived Intangible Assets
Gross Carrying Amount	2,233		2,233
Accumulated Amortization	764		710
Net Book Value	1,469		$ 1,523	[1]
Amortization expense	54	$ 55
Estimated future annual amortization expense
Remainder of 2019	165
2020	191
2021	185
2022	185
2023	185
Thereafter	541
Total	1,452
Impairment Analysis
Impairment charges recognized	$ 0	$ 0
Customer Relationships
Finite-Lived Intangible Assets
Remaining lives	9 years		9 years
Gross Carrying Amount	$ 1,302		$ 1,302
Accumulated Amortization	542		506
Net Book Value	$ 760		$ 796
Intellectual Property
Finite-Lived Intangible Assets
Remaining lives	3 years		3 years
Gross Carrying Amount	$ 100		$ 100
Accumulated Amortization	69		61
Net Book Value	$ 31		$ 39
Trade Names
Finite-Lived Intangible Assets
Remaining lives	20 years		20 years
Gross Carrying Amount	$ 814		$ 814
Accumulated Amortization	153		143
Net Book Value	$ 661		$ 671
Patents
Finite-Lived Intangible Assets
Remaining lives	7 years		7 years
Gross Carrying Amount	$ 17		$ 17
Net Book Value	$ 17		$ 17

[1] The balance sheet at December 31, 2018 has been derived from the audited financial statements at that date.