SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)		12 Months Ended
	Aug. 15, 2017 USD ($)	Dec. 31, 2018 USD ($) reporting_unit	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Aug. 14, 2017 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Capitalized cost of internal-use software		$ 3,500,000	$ 4,400,000	$ 4,300,000
Unamortized software costs		12,700,000	17,900,000
Amortization expense capitalized		$ 7,600,000	7,200,000	8,300,000
Number of reporting units | reporting_unit		7
Amortization of intangible assets		$ 4,034,000	2,147,000	3,048,000
Uncertain tax positions recognized		500,000	200,000
Research and development costs		2,800,000	1,500,000	1,100,000
Excluded capitalized cost of internal-use software		5,200,000	5,200,000	6,300,000
Advertising costs		$ 2,600,000	$ 1,900,000	$ 2,100,000
Customer relationships
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets		5 years	5 years	6 years
Network equipment
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets		5 years
Minimum
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets		5 years
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
Minimum | Furniture Equipment and Software
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets		3 years
Minimum | Leasehold improvements
Summary Of Significant Accounting Policy [Line Items]
Duration of lease obligations and commitments		2 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		15 years
Maximum | Furniture Equipment and Software
Summary Of Significant Accounting Policy [Line Items]
Estimated useful lives of assets		7 years
Maximum | Leasehold improvements
Summary Of Significant Accounting Policy [Line Items]
Duration of lease obligations and commitments		34 years
Internap Japan Investment
Summary Of Significant Accounting Policy [Line Items]
Investment in joint venture					$ 4,100,000
Internap Japan
Summary Of Significant Accounting Policy [Line Items]
Ownership percentage		66.63%
Internap Japan
Summary Of Significant Accounting Policy [Line Items]
Gain recognized	$ 1,100,000
Service and Renewal Contracts
Summary Of Significant Accounting Policy [Line Items]
Capitalized contract cost		$ 24,900,000
Capitalized contract cost, amortization		9,600,000
Capitalized contract cost, impairment		$ 0