SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)			1 Months Ended	3 Months Ended												6 Months Ended			9 Months Ended			12 Months Ended
	Aug. 01, 2019 USD ($)	Aug. 15, 2017 USD ($)	Aug. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) reporting_unit	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Aug. 01, 2020	Mar. 13, 2020 USD ($)	Dec. 25, 2019 USD ($)	Dec. 01, 2019	Jan. 15, 2019 USD ($)	Jan. 01, 2019 USD ($)	Aug. 14, 2017 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Net loss					$ 24,083,000	$ 17,982,000	$ 20,007,000	$ 18,880,000	$ 14,840,000	$ 13,802,000	$ 13,678,000	$ 6,649,000	$ 10,647,000	$ 18,894,000	$ 8,046,000	$ 37,989,000	$ 27,480,000	$ 26,940,000	$ 62,072,000	$ 42,320,000	$ 37,587,000	$ 138,250,000	$ 61,200,000	$ 44,236,000
Working capital deficit				$ 442,000,000				6,500,000														442,000,000	6,500,000
Term loan amount				425,900,000																		425,900,000
Capitalized cost of internal-use software																						3,300,000	3,500,000	4,400,000
Unamortized software costs				11,000,000				12,700,000														11,000,000	12,700,000
Amortization expense capitalized																						$ 5,500,000	7,600,000	7,200,000
Number of reporting units | reporting_unit																						7
Amortization of intangible assets																						$ 4,501,000	4,034,000	2,147,000
Goodwill and intangibles impairment			$ 0																			$ 45,009,000	0
Percentage of goodwill impaired																						25.00%
Impairment of intangible assets																						$ 14,100,000
Impairment of intangible assets	$ 0
Capitalized contract cost, impairment loss																						0	0
Research and development costs																						2,100,000	2,800,000	1,500,000
Excluded capitalized cost of internal-use software																						4,200,000	5,200,000	5,200,000
Advertising costs																						2,200,000	$ 2,600,000	$ 1,900,000
Operating lease right-of-use assets				62,537,000																		62,537,000								$ 28,500,000
Total lease liabilities				81,542,000																		81,542,000								$ 31,000,000
Customer relationships and trade names
Summary Of Significant Accounting Policy [Line Items]
Impairment of intangible assets																						13,100,000
Developed technology
Summary Of Significant Accounting Policy [Line Items]
Impairment of intangible assets																						$ 1,000,000
Customer relationships
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						5 years	5 years	5 years
Impairment of intangible assets																						$ 200,000
Minimum | Acquired Technologies and Noncompete Agreements
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						4 years
Minimum | Trade names
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						8 years
Minimum | Customer relationships and trade names
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						10 years
Maximum | Acquired Technologies and Noncompete Agreements
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						8 years
Maximum | Trade names
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						15 years
Maximum | Customer relationships and trade names
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets																						30 years
Network equipment
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets																						5 years
Furniture Equipment and Software | Minimum
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets																						3 years
Furniture Equipment and Software | Maximum
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets																						7 years
Leasehold improvements | Minimum
Summary Of Significant Accounting Policy [Line Items]
Duration of lease obligations and commitments																						2 years
Leasehold improvements | Maximum
Summary Of Significant Accounting Policy [Line Items]
Duration of lease obligations and commitments																						34 years
Fulfillment Costs And Commission Fees
Summary Of Significant Accounting Policy [Line Items]
Capitalized contract cost				23,900,000				24,900,000														$ 23,900,000	$ 24,900,000
Amortization of capitalized contract costs																						9,900,000	9,600,000
Put Option
Summary Of Significant Accounting Policy [Line Items]
Settlement alternatives, cash at fair value																											$ 500,000		$ 1,000,000
INAP
Summary Of Significant Accounting Policy [Line Items]
Ownership percentage																													85.00%
NTT ME
Summary Of Significant Accounting Policy [Line Items]
Ownership percentage by noncontrolling owners																													15.00%
Internap Japan
Summary Of Significant Accounting Policy [Line Items]
Gain recognized		$ 1,100,000
Internap Japan Investment
Summary Of Significant Accounting Policy [Line Items]
Equity investment																															$ 4,100,000
Reclassification | Adjustment
Summary Of Significant Accounting Policy [Line Items]
Net loss					$ 213,000	$ (573,000)	$ 363,000	426,000	$ (639,000)	$ (477,000)	$ (610,000)	$ (285,000)	$ (248,000)	$ (389,000)	$ (184,000)	$ (210,000)	$ (1,087,000)	$ (573,000)	$ 3,000	$ (1,726,000)	$ (822,000)		(1,300,000)	$ (1,107,000)
Depreciation and amortization																						1,500,000	2,000,000	$ 1,600,000
Property and equipment, net				1,500,000				4,100,000														1,500,000	4,100,000
Reclassification | Cumulative Income of Prior Period Adjustments
Summary Of Significant Accounting Policy [Line Items]
Property and equipment, net								$ 2,100,000															$ 2,100,000
INAP CLOUD
Summary Of Significant Accounting Policy [Line Items]
Goodwill and intangibles impairment				22,900,000
Impairment of intangible assets																						12,900,000
Cloud INAP INTL
Summary Of Significant Accounting Policy [Line Items]
Goodwill and intangibles impairment				21,200,000
Ubersmith INAP INTL
Summary Of Significant Accounting Policy [Line Items]
Goodwill and intangibles impairment				900,000
Impairment of intangible assets																						1,200,000
Measurement Input, Discount Rate | Minimum
Summary Of Significant Accounting Policy [Line Items]
Measurement input																												0.120
Measurement Input, Discount Rate | Maximum
Summary Of Significant Accounting Policy [Line Items]
Measurement input																												0.160
Subsequent Event
Summary Of Significant Accounting Policy [Line Items]
Term loan amount																										$ 5,000,000
Subsequent Event | Measurement Input, Discount Rate | Minimum
Summary Of Significant Accounting Policy [Line Items]
Measurement input																									0.080
Subsequent Event | Measurement Input, Discount Rate | Maximum
Summary Of Significant Accounting Policy [Line Items]
Measurement input																									0.130
Subsequent Event | Measurement Input, Long-term Revenue Growth Rate | Minimum
Summary Of Significant Accounting Policy [Line Items]
Measurement input																									0.020
Subsequent Event | Measurement Input, Long-term Revenue Growth Rate | Maximum
Summary Of Significant Accounting Policy [Line Items]
Measurement input																									0.010
Current Liabilities
Summary Of Significant Accounting Policy [Line Items]
Term loan amount				$ 413,300,000.0																		$ 413,300,000.0