REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 325,176	$ 333,532	$ 650,838	$ 672,181
Receivables, contract assets and contract liabilities
Accounts receivable, net	116,493	133,535	116,493	133,535
Contract assets	20,130	15,991	20,130	15,991
Contract liabilities	50,296	51,406	50,296	51,406
Recognized expenses related to deferred contract acquisition costs.	2,200	1,500	4,300	2,700
Recognized revenue related to deferred revenue	109,900	92,700	$ 221,100	186,700
Revenue, Practical Expedient, Remaining Performance Obligation			true
Minimum
Receivables, contract assets and contract liabilities
Payment term			30 days
Maximum
Receivables, contract assets and contract liabilities
Payment term			60 days
Commercial and carrier
Disaggregation of Revenue [Line Items]
Total operating revenues	145,753	149,064	$ 292,757	300,436
Commercial and carrier - Data and transport services (including VoIP)
Disaggregation of Revenue [Line Items]
Total operating revenues	89,572	88,538	179,144	176,664
Commercial and carrier - Voice services
Disaggregation of Revenue [Line Items]
Total operating revenues	45,775	47,136	91,495	95,206
Commercial and carrier - Other
Disaggregation of Revenue [Line Items]
Total operating revenues	10,406	13,390	22,118	28,566
Subsidies
Disaggregation of Revenue [Line Items]
Total operating revenues	18,069	18,134	36,523	36,293
Consumer
Disaggregation of Revenue [Line Items]
Total operating revenues	127,901	129,644	254,284	259,344
Consumer - Broadband (VoIP and Data)
Disaggregation of Revenue [Line Items]
Total operating revenues	65,567	64,068	129,643	127,153
Consumer - Video services
Disaggregation of Revenue [Line Items]
Total operating revenues	19,213	20,341	38,344	41,077
Consumer - Voice services
Disaggregation of Revenue [Line Items]
Total operating revenues	43,121	45,235	86,297	91,114
Network access
Disaggregation of Revenue [Line Items]
Total operating revenues	30,473	34,198	61,938	70,789
Other products and services
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 2,980	$ 2,492	$ 5,336	$ 5,319