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ACQUISITIONS AND DISPOSITIONS - Pro Forma Results (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 01, 2016
Acquisition
Impairment charges	$ 0	$ 0	$ 11,425
One Communications (formerly KeyTech)
Acquisition
Retirement of debt			24,700
Viya (formerly Innovative)
Acquisition
Retirement of debt			185,800
Viya (formerly Innovative) \| Term loans
Acquisition
Debt instrument, face amount					$ 60,000
One Communications and Viya
Pro Forma
Revenue			457,003	$ 355,369
Net income (loss) attributable to ATN International, Inc. Stockholders			$ 12,101	$ 16,940
Earnings per share: Basic (in dollars per share)			$ 0.75	$ 1.06
Earnings per share: Diluted (in dollars per share)			$ 0.75	$ 1.05
One Communications and Viya \| Previously Reported
Pro Forma
Revenue			$ 535,628	$ 546,589
Net income (loss) attributable to ATN International, Inc. Stockholders			$ 14,660	$ (97,102)
Earnings per share: Basic (in dollars per share)			$ 0.91	$ (6.06)
Earnings per share: Diluted (in dollars per share)			$ 0.90	$ (6.02)
One Communications and Viya
Acquisition
Impairment charges			$ 5,400	$ 168,700
One Communications (formerly KeyTech)
Acquisition
Impairment charges				85,600
Viya (formerly Innovative)
Acquisition
Impairment charges				$ 83,100