SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands		12 Months Ended
	Aug. 15, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) reporting_unit	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Aug. 14, 2017 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Carrying value of debt		$ 303,500	$ 303,500	$ 303,500	$ 303,500	$ 303,500
Fair value of debt		306,500	306,500	306,500	306,500	306,500
Capitalized cost of internal-use software			4,400				$ 4,300	$ 4,600
Unamortized software costs		17,900	17,900	$ 17,900	17,900	17,900	20,000
Amortization expense capitalized			7,200				8,300	6,600
Number of reporting units | reporting_unit				6
Amortization of intangible assets			2,147				3,048	3,450
Uncertain tax positions		200	200	$ 200	$ 200	$ 200	200
Research and development costs			1,500				1,100	2,200
Excluded capitalized cost of internal-use software			5,200				6,300	6,500
Advertising costs			1,900				2,100	4,900
Number of operating segments					2	2
Deferred tax assets		131,061	131,061	131,061	$ 131,061	$ 131,061	163,352
Deferred tax asset, Valuation allowance		132,712	132,712	132,712	132,712	132,712	164,865	$ 148,310		$ 136,017
Retained earnings		$ (1,323,723)	(1,323,723)	(1,323,723)	(1,323,723)	(1,323,723)	$ (1,278,699)
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 (in years)		5 years
Minimum
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets		5 years
Minimum | Acquired technology
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets		5 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 (in years)		3 years
Minimum | Leasehold improvements
Summary Of Significant Accounting Policy [Line Items]
Duration of lease obligations and commitments		3 years
Maximum
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets		15 years
Maximum | Acquired technology
Summary Of Significant Accounting Policy [Line Items]
Amortized period of assets		8 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 (in years)		7 years
Maximum | Leasehold improvements
Summary Of Significant Accounting Policy [Line Items]
Duration of lease obligations and commitments		25 years
Internap Japan Investment
Summary Of Significant Accounting Policy [Line Items]
Investment in joint venture									$ 4,100
Internap Japan
Summary Of Significant Accounting Policy [Line Items]
Gain recognized	$ 1,100
Accounting Standards Update 2016-16
Summary Of Significant Accounting Policy [Line Items]
Deferred tax assets							$ 2,200
Deferred tax asset, Valuation allowance							1,900
Accounting Standards Update 2016-09
Summary Of Significant Accounting Policy [Line Items]
Deferred tax assets							10,800
Deferred tax asset, Valuation allowance							$ 10,800
Pro Forma | Difference Between Revenue Guidance In Effect Before And After Topic 606 | Accounting Standards Update 2014-09
Summary Of Significant Accounting Policy [Line Items]
Retained earnings		$ 23,600	$ 23,600	$ 23,600	$ 23,600	$ 23,600