REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 333,532	$ 350,221	$ 672,181	$ 706,260
Receivables, contract assets and contract liabilities
Accounts receivable, net	133,535	122,411	133,535	122,411
Contract assets	15,991	7,408	15,991	7,408
Contract liabilities	51,406	49,039	51,406	49,039
Recognized expenses related to deferred contract acquisition costs.	1,500	600	2,700	1,000
Recognized revenue related to deferred revenue	92,700	83,800	$ 186,700	171,100
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	149,064	153,162	$ 300,436	303,211
Commercial and carrier - Data and transport services (including VoIP)
Disaggregation of Revenue [Line Items]
Total operating revenues	88,538	87,603	176,664	173,628
Commercial and carrier - Voice services
Disaggregation of Revenue [Line Items]
Total operating revenues	47,136	51,322	95,206	103,483
Commercial and carrier - Other
Disaggregation of Revenue [Line Items]
Total operating revenues	13,390	14,237	28,566	26,100
Subsidies
Disaggregation of Revenue [Line Items]
Total operating revenues	18,134	20,979	36,293	46,234
Consumer
Disaggregation of Revenue [Line Items]
Total operating revenues	129,644	136,226	259,344	274,233
Consumer - Broadband (VoIP and Data)
Disaggregation of Revenue [Line Items]
Total operating revenues	64,068	62,545	127,153	125,656
Consumer - Video services
Disaggregation of Revenue [Line Items]
Total operating revenues	20,341	22,065	41,077	44,899
Consumer - Voice services
Disaggregation of Revenue [Line Items]
Total operating revenues	45,235	51,616	91,114	103,678
Network access
Disaggregation of Revenue [Line Items]
Total operating revenues	34,198	37,338	70,789	77,053
Other products and services
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 2,492	$ 2,516	$ 5,319	$ 5,529