CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								6 Months Ended		9 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	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net sales	$ 138,234	$ 136,318	$ 127,073	$ 94,413	$ 131,476	$ 99,953	$ 100,922	$ 84,265					$ 496,038	$ 416,616
Cost of sales	126,213	117,510	109,006	84,540	115,981	86,702	88,443	74,497					437,269	365,623
Gross profit	12,021	18,808	18,067	9,873	15,495	13,251	12,479	9,768					58,769	50,993
Operating expenses:
Research, development and engineering expenses	7,910	7,708	6,962	6,021	6,459	5,687	3,848	3,950					28,601	19,944
Selling, general and administrative expenses	16,727	16,374	13,276	13,254	11,297	12,062	10,688	10,209					59,631	44,256
Asset impairment charges	2,234	0	0	0	1	0	0	0					2,234	1
Amortization of intangible assets	1,321	1,321	1,321	1,045	1,210	1,210	1,209	1,209					5,008	4,838
Total operating expenses	28,192	25,403	21,559	20,320	18,967	18,959	15,745	15,368					95,474	69,039
Operating loss	(16,171)	(6,595)	(3,492)	(10,447)	(3,472)	(5,708)	(3,266)	(5,600)					(36,705)	(18,046)
Other expense (income):
Interest expense	2,203	1,974	1,828	1,623	1,703	1,654	1,404	6,080					7,628	10,841
Loss from change in fair value of warrants	(8,800)	10,200	6,500	2,500	1,500	1,700	800	0					10,400	4,000
Loss on debt extinguishment and modifications					0	0	0	11,921					0	11,921
Other expense (income), net	81	(68)	(95)	(94)	(226)	(10)	2,142	455					(176)	2,361
Total other expense (income)	(6,516)	12,106	8,233	4,029	2,977	3,344	4,346	18,456					17,852	29,123
Loss before income taxes	(9,655)	(18,701)	(11,725)	(14,476)	(6,449)	(9,052)	(7,612)	(24,056)					(54,557)	(47,169)
Income tax expense	243	118	80	(272)	(320)	149	135	479					169	443
Net loss	$ (9,898)	$ (18,819)	$ (11,805)	$ (14,204)	(6,129)	(9,201)	(7,747)	(24,535)	$ (26,009)	$ (32,282)	$ (44,828)	$ (41,483)	(54,726)	(47,612)
Deemed dividend on Series B convertible preferred stock					(31,067)	(3,603)	(3,190)	0					0	(37,860)
Net loss available to common stockholders					$ (37,196)	$ (12,804)	$ (10,937)	$ (24,535)					$ (54,726)	$ (85,472)
Weighted-average common shares outstanding:
Basic (in shares)	18,638	18,625	18,594	18,483	16,774	13,659	13,697	11,018					18,585	13,787
Diluted (in shares)	22,360	18,625	18,594	18,483	16,774	13,659	13,697	11,018					18,585	13,787
Loss per common share:
Basic (in dollars per share)	$ (0.53)	$ (1.01)	$ (0.63)	$ (0.77)	$ (2.22)	$ (0.94)	$ (0.80)	$ (2.23)					$ (2.94)	$ (6.20)
Diluted (in dollars per share)	$ (0.84)	$ (1.01)	$ (0.63)	$ (0.77)	$ (2.22)	$ (0.94)	$ (0.80)	$ (2.23)					$ (2.94)	$ (6.20)