SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Current Impact from Adoption on Consolidated Income Statements (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
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
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
Sales, general and administrative											75,356,000	62,728,000	70,639,000
Total Expense Reduction											311,217,000	275,944,000	391,367,000
Income (loss) from operations											6,156,000	4,774,000	(93,070,000)
Loss from continuing operations before income taxes, non-controlling interest and equity in (earnings) of equity-method investment											(61,718,000)	(46,227,000)	(124,382,000)
Net loss											(62,375,000)	(45,273,000)	(124,742,000)
Less net income attributable to non-controlling interest											(125,000)	(70,000)	0
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)
Comprehensive loss											(62,241,000)	$ (45,175,000)	$ (123,453,000)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues											316,606,000
Sales, general and administrative											75,120,000
Total Expense Reduction											310,981,000
Income (loss) from operations											5,625,000
Loss from continuing operations before income taxes, non-controlling interest and equity in (earnings) of equity-method investment											(62,249,000)
Net loss											(62,906,000)
Less net income attributable to non-controlling interest											(125,000)
Net loss attributable to INAP shareholders											(63,031,000)
Comprehensive loss											(62,772,000)
Accounting Standards Update 2014-09 | Difference Between Revenue Guidance In Effect Before And After Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues											767,000
Sales, general and administrative											236,000
Total Expense Reduction											236,000
Income (loss) from operations											531,000
Loss from continuing operations before income taxes, non-controlling interest and equity in (earnings) of equity-method investment											531,000
Net loss											531,000
Less net income attributable to non-controlling interest											0
Net loss attributable to INAP shareholders											531,000
Comprehensive loss											$ 531,000