UNAUDITED QUARTERLY RESULTS - Summary of Unaudited Quarterly Data (Details) - USD ($)	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended			50 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	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 78,238,000	$ 82,972,000	$ 81,962,000	$ 74,201,000	$ 70,035,000	$ 68,907,000	$ 69,642,000	$ 72,133,000			$ 317,373,000	$ 280,718,000	$ 298,297,000	$ 8,855
Costs of sales and services, exclusive of depreciation and amortization	23,662,000	29,511,000	28,621,000	25,467,000	25,798,000	24,945,000	26,429,000	29,045,000	$ 54,088,000	$ 83,601,000	107,262,000	106,217,000	124,255,000
Costs of customer support	8,305,000	7,984,000	8,841,000	7,387,000	6,122,000	6,237,000	6,133,000	7,264,000			32,517,000	25,757,000	32,184,000
Exit activities, restructuring and impairments	2,266,000	2,347,000	826,000	(33,000)	(148,000)	745,000	4,628,000	1,023,000			5,406,000	6,249,000	7,236,000
Net loss attributable to INAP shareholders	$ (18,454,000)	$ (15,479,000)	$ (14,279,000)	$ (14,288,000)	$ (6,934,000)	$ (10,895,000)	$ (19,283,000)	$ (8,230,000)	$ (28,567,000)	$ (44,046,000)	$ (62,500,000)	$ (45,343,000)	$ (124,742,000)
Basic and diluted net loss per share (in dollars per share)	$ (0.82)	$ (0.75)	$ (0.69)	$ (0.70)	$ (0.35)	$ (0.55)	$ (0.97)	$ (0.51)			$ (3.01)	$ (2.39)	$ (9.54)