REVENUE (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 318,480	$ 318,584	$ 320,403	$ 324,766	$ 326,124	$ 327,066	$ 325,176	$ 325,662	$ 1,282,233	$ 1,304,028	$ 1,336,542
Receivables, contract assets and contract liabilities
Accounts receivable, net	133,362				137,646				133,362	137,646
Contract assets	23,893				21,004				23,893	21,004
Contract liabilities	$ 60,503				$ 55,942				60,503	55,942
Recognized expenses related to deferred contract acquisition costs.									11,100	9,000	6,300
Revenue recognized from beginning of year and current period increase in contract liability									$ 471,700	443,000	397,500
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									$ 575,739	588,933	596,541
Commercial and carrier - Data and transport services (including VoIP)
Disaggregation of Revenue [Line Items]
Total operating revenues									362,365	362,078	355,325
Commercial and carrier - Voice services
Disaggregation of Revenue [Line Items]
Total operating revenues									171,750	181,700	188,322
Commercial and carrier - Other
Disaggregation of Revenue [Line Items]
Total operating revenues									41,624	45,155	52,894
Consumer
Disaggregation of Revenue [Line Items]
Total operating revenues									495,135	507,905	519,300
Consumer - Broadband (VoIP and Data)
Disaggregation of Revenue [Line Items]
Total operating revenues									269,323	263,059	257,083
Consumer - Video services
Disaggregation of Revenue [Line Items]
Total operating revenues									65,114	74,343	81,378
Consumer - Voice services
Disaggregation of Revenue [Line Items]
Total operating revenues									160,698	170,503	180,839
Subsidies
Disaggregation of Revenue [Line Items]
Total operating revenues									69,739	71,989	72,440
Network access
Disaggregation of Revenue [Line Items]
Total operating revenues									120,487	125,261	138,056
Other products and services
Disaggregation of Revenue [Line Items]
Total operating revenues									$ 21,133	$ 9,940	$ 10,205