ACQUISITION - Unaudited Pro-Forma Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Business Combinations [Abstract]
Revenue	$ 325,498	$ 328,572
Net loss attributable to INAP stockholders	$ (63,577)	$ (47,391)
Basic and diluted net loss per share (in dollars per share)	$ (3.07)	$ (2.50)
Weighted average shares outstanding used in computing basic and diluted net loss per share (in shares)	20,732	18,993