BUSINESS DESCRIPTION & SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Property, plant and equipment
Total plant in service	$ 4,756,696	$ 4,387,847
Less: accumulated depreciation and amortization	(2,754,587)	(2,698,421)
Plant in service	2,002,109	1,689,426
Totals	2,234,122	2,019,444
Depreciation and amortization expense	$ 269,300	261,100	$ 274,200
Internal use network and non-network software | Maximum
Property, plant and equipment
Period after which property plan and equipment capitalized	1 year
Land and buildings
Property, plant and equipment
Total plant in service	$ 270,708	276,027
Land and buildings | Minimum
Property, plant and equipment
Estimated Useful Lives	18 years
Land and buildings | Maximum
Property, plant and equipment
Estimated Useful Lives	40 years
Central office switching and transmission
Property, plant and equipment
Total plant in service	$ 1,635,263	1,590,510
Central office switching and transmission | Minimum
Property, plant and equipment
Estimated Useful Lives	3 years
Central office switching and transmission | Maximum
Property, plant and equipment
Estimated Useful Lives	25 years
Outside plant cable, wire and fiber facilities
Property, plant and equipment
Total plant in service	$ 2,445,298	2,152,253
Outside plant cable, wire and fiber facilities | Minimum
Property, plant and equipment
Estimated Useful Lives	3 years
Outside plant cable, wire and fiber facilities | Maximum
Property, plant and equipment
Estimated Useful Lives	50 years
Furniture, fixtures and equipment
Property, plant and equipment
Total plant in service	$ 347,346	324,562
Furniture, fixtures and equipment | Minimum
Property, plant and equipment
Estimated Useful Lives	3 years
Furniture, fixtures and equipment | Maximum
Property, plant and equipment
Estimated Useful Lives	15 years
Assets under finance leases
Property, plant and equipment
Total plant in service	$ 58,081	44,495
Assets under finance leases | Minimum
Property, plant and equipment
Estimated Useful Lives	2 years
Assets under finance leases | Maximum
Property, plant and equipment
Estimated Useful Lives	20 years
Construction in progress
Property, plant and equipment
Total plant in service	$ 123,736	265,054
Construction inventory
Property, plant and equipment
Total plant in service	$ 108,277	$ 64,964