UNAUDITED QUARTERLY INFORMATION (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
UNAUDITED QUARTERLY INFORMATION
Net Sales	$ 66,612	$ 68,349	$ 68,038	$ 66,555	$ 54,287	$ 51,929	$ 60,354	$ 49,929	$ 269,554	$ 216,499	$ 209,240
Gross Profit	29,135	30,135	27,785	25,869	20,361	20,970	24,248	18,561
Operating income (loss)	3,956	3,474	546	1,181	(8,557)	2,616	3,217	132	9,157	(2,592)	9,615
Other expense, net	(1,727)	(1,812)	(1,774)	(1,744)	(866)	(634)	(320)	(912)
(Loss) income from operations	2,229	1,662	(1,228)	(563)	(9,423)	1,982	2,897	(780)	2,100	(5,324)	8,143
Net (loss) income attributable to ISG	$ (2,650)	$ 1,428	$ (302)	$ (606)	$ (8,150)	$ 732	$ 1,612	$ (699)	$ (2,130)	$ (6,505)	$ 4,841
Basic (loss) earnings per share attributable to ISG	$ (0.06)	$ 0.03	$ (0.01)	$ (0.01)	$ (0.22)	$ 0.02	$ 0.05	$ (0.02)	$ (0.05)	$ (0.18)	$ 0.13
Diluted (loss) earnings per share attributable to ISG	$ (0.06)	$ 0.03	$ (0.01)	$ (0.01)	$ (0.22)	$ 0.02	$ 0.04	$ (0.02)	$ (0.05)	$ (0.18)	$ 0.13
Basic weighted average common shares	43,423	43,305	43,058	42,316	37,842	35,707	35,609	37,340	43,025	36,625	37,186
Diluted weighted average common shares	43,423	44,658	43,058	42,316	37,842	36,873	36,719	37,340	43,025	36,625	38,936