Quarterly information (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues									$ 709,431	$ 528,614	$ 266,687
Gross profit	$ 20,462	$ 27,291	$ 34,900	$ 24,730	$ 16,905	$ 24,182	$ 26,318	$ 15,883	107,383	83,288	51,194
Selling, general, and administrative expenses	28,867	29,345	24,450	20,538	18,728	17,621	16,943	18,968	103,200	72,260	37,905
Operating income (loss)	(12,635)	(4,364)	8,990	4,872	(4,853)	6,911	8,916	(3,226)	(3,137)	7,748	13,289
Net (loss) income	$ (13,752)	$ (8,796)	$ 5,918	$ 2,326	$ (5,256)	$ 3,902	$ 5,398	$ (3,957)	$ (14,302)	$ 87	$ 7,817
Basic net income (loss) per common share	$ (0.47)	$ (0.26)	$ 0.17	$ 0.07	$ (0.16)	$ 0.13	$ 0.16	$ (0.14)	$ (0.51)	$ (0.05)	$ (0.26)
Diluted net (loss) income per common share	$ (0.47)	$ (0.26)	$ 0.17	$ 0.07	$ (0.16)	$ 0.13	$ 0.16	$ (0.14)	$ (0.51)	$ (0.05)	$ (0.26)
Basic weighted average shares (in shares)	23,436	22,974	22,365	21,800	21,283	16,944	15,980	14,575	22,652	17,216	13,223
Diluted weighted average shares (in shares)	23,436	22,974	22,597	21,978	21,283	17,239	16,008	14,575	22,652	17,216	13,223
Product
Revenues	$ 134,894	$ 161,534	$ 194,606	$ 126,084	$ 95,141	$ 108,524	$ 148,713	$ 97,851	$ 617,118	$ 450,229	$ 266,687
Services
Revenues	$ 19,442	$ 24,491	$ 26,028	$ 22,352	$ 15,883	$ 22,858	$ 22,429	$ 17,215	$ 92,313	$ 78,385