LEASES - Maturities of lease liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
LEASES
2021 (excluding the six months ended June 30, 2021)	$ 8,184
Next Twelve Months	15,243	$ 14,877
Year Two	12,846	14,202
Year Three	11,702	11,799
Year Four	8,800	10,633
Thereafter	14,599
Year Five		7,816
Thereafter		13,094
Total lease payments	71,374	72,421
Less imputed interest	(9,323)	(10,097)
Total	$ 62,051	$ 62,324
Operating Lease, Liability, Statement of Financial Position [Extensible List]	atni:LeaseLiabilityCurrent atni:LeaseLiabilityNoncurrent	atni:LeaseLiabilityCurrent atni:LeaseLiabilityNoncurrent
Finance lease liability
2021 (excluding the six months ended June 30, 2021)	$ 251
Next Twelve Months	501	$ 334
Year two	501	333
Year three	383	333
Year four	285	211
Thereafter	522
Total lease payments	2,443	1,211
Less imputed interest	(317)	(82)
Total	$ 2,126	$ 1,129
Finance Lease, Liability, Statement of Financial Position [Extensible List]	atni:LeaseLiabilityCurrent atni:LeaseLiabilityNoncurrent	atni:LeaseLiabilityCurrent atni:LeaseLiabilityNoncurrent