NET INCOME PER COMMON SHARE - Computation of Earnings Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Basic:                      
Net income attributable to ISG $ 1,276 $ 1,778 $ 934 $ 853 $ 657 $ 2,353 $ 3,105 $ 63 $ 4,841 $ 6,178 $ 4,776
Weighted average common shares 37,198 37,315 37,199 37,032 36,702 37,039 37,220 37,383 37,186 37,086 36,810
Earnings per share attributable to ISG $ 0.03 $ 0.05 $ 0.03 $ 0.02 $ 0.02 $ 0.06 $ 0.08 $ 0.00 $ 0.13 $ 0.17 $ 0.13
Diluted:                      
Net income attributable to ISG $ 1,276 $ 1,778 $ 934 $ 853 $ 657 $ 2,353 $ 3,105 $ 63 $ 4,841 $ 6,178 $ 4,776
Interest expense of convertible debt, net of tax                 80 80 108
Net income, attributable to ISG, as adjusted                 $ 4,921 $ 6,258 $ 4,884
Basic Weighted Average Common shares 37,198 37,315 37,199 37,032 36,702 37,039 37,220 37,383 37,186 37,086 36,810
Potential common shares                 1,750 1,607 1,877
Diluted weighted average common shares 38,986 39,296 38,971 38,490 38,333 38,740 38,837 38,861 38,936 38,693 38,687
Diluted earnings per share attributable to ISG $ 0.03 $ 0.05 $ 0.02 $ 0.02 $ 0.02 $ 0.06 $ 0.08 $ 0.00 $ 0.13 $ 0.16 $ 0.13