NET LOSS PER SHARE - Schedule of basic and diluted net loss per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (15,081)	$ (10,863)	$ (43,014)	$ (38,377)
Less net income attributable to non-controlling interest	25	32	75	32
Net loss attributable to INAP stockholders	$ (15,106)	$ (10,895)	$ (43,089)	$ (38,409)
Weighted average shares outstanding, basic and diluted (in shares)	20,206	19,929	19,968	18,645
Net loss per share, basic and diluted (in dollars per share)	$ (0.75)	$ (0.56)	$ (2.16)	$ (2.04)
Anti-dilutive securities excluded from diluted net loss per share calculation for stock-based compensation plans (in shares)	1,065	1,460	1,065	1,460