QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly financial data
Total revenue	$ 123,702	$ 111,739	$ 109,098	$ 110,905	$ 112,085	$ 115,616	$ 107,721	$ 103,300	$ 455,444	$ 438,722	$ 451,207
Operating expenses	138,402	102,182	102,074	103,606	113,824	105,368	104,967	101,186	446,264	425,345	390,184
Income from operations	(14,700)	9,557	7,024	7,299	(1,739)	10,248	2,754	2,114	9,180	13,377	61,023
Other income (expense), net	(1,081)	(3,274)	(918)	(3,814)	(2,568)	(3,570)	(1,001)	(166)	(9,087)	(7,305)	(7,281)
INCOME BEFORE INCOME TAXES	(15,781)	6,283	6,106	3,485	(4,307)	6,678	1,753	1,948	93	6,072	53,742
Income taxes	1,858	92	(2,258)	1,109	1,332	1,834	(274)	1,213	801	4,105	18,870
NET INCOME	(17,639)	6,191	8,364	2,376	(5,639)	4,844	2,027	735	(708)	1,967	34,872
Net income attributable to non-controlling interests, net of tax	(2,876)	(3,530)	(3,618)	(3,390)	(4,115)	(3,459)	(2,883)	(2,316)	(13,414)	(12,773)	(15,057)
NET INCOME (LOSS) ATTRIBUTABLE TO ATN INTERNATIONAL, INC. STOCKHOLDERS	$ (20,515)	$ 2,661	$ 4,746	$ (1,014)	$ (9,754)	$ 1,385	$ (856)	$ (1,581)	$ (14,122)	$ (10,806)	$ 19,815
NET INCOME (LOSS) PER WEIGHTED AVERAGE SHARE ATTRIBUTABLE TO ATN INTERNATIONAL, INC. STOCKHOLDERS:
Basic (in dollars per share)	$ (1.30)	$ 0.17	$ 0.30	$ (0.06)	$ (0.62)	$ 0.09	$ (0.05)	$ (0.10)	$ (0.89)	$ (0.68)	$ 1.24
Diluted (in dollars per share)	$ (1.30)	$ 0.17	$ 0.30	$ (0.06)	$ (0.62)	$ 0.09	$ (0.05)	$ (0.10)	$ (0.89)	$ (0.68)	$ 1.24