BUSINESS DESCRIPTION & SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, plant and equipment
Total plant in service	$ 4,387,847	$ 4,130,524
Less: accumulated depreciation and amortization	(2,698,421)	(2,466,407)
Plant in service	1,689,426	1,664,117
Totals	2,019,444	1,760,152
Depreciation and amortization expense	$ 261,100	274,200	$ 315,000
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	$ 276,027	274,535
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	$ 1,590,510	1,475,590
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	$ 2,152,253	2,036,312
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	$ 324,562	303,680
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	$ 44,495	40,407
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	$ 265,054	64,056
Construction inventory
Property, plant and equipment
Total plant in service	$ 64,964	$ 31,979