COMMITMENTS AND CONTINGENCIES - Litigation (Details) $ in Thousands			3 Months Ended		12 Months Ended	108 Months Ended	171 Months Ended
	Aug. 15, 2018 USD ($)	Jul. 17, 2018 USD ($)	Mar. 31, 2020 USD ($) item subsidiary	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2020 USD ($)	May 31, 2017 USD ($)
Litigation and Contingencies
Revenue recorded			$ 325,662	$ 338,649
Number of subsidiaries that received assessment notice | subsidiary			2
Consolidated Communications Enterprise Services Inc. (CCES)
Litigation and Contingencies
Litigation amount accrued			$ 1,500				$ 1,500
Consolidated Communications of Pennsylvania Company LLC (CCPA)
Litigation and Contingencies
Litigation amount accrued			$ 700				700
Sprint, MCI Communication Services, and Verizon
Litigation and Contingencies
Disputed amount							$ 4,800
Number of courts | item			1
Level 3 Communications
Litigation and Contingencies
Disputed amount					$ 2,300
Amount awarded		$ 700
FairPoint Communications, Inc | Level 3 Communications
Litigation and Contingencies
Amount awarded	$ 1,200
Subsidies
Litigation and Contingencies
Revenue recorded			$ 18,454	$ 18,159
Assessment by Commonwealth of Pennsylvania Department of Revenue | Maximum
Litigation and Contingencies
Potential liability amount guaranteed								$ 5,000
Assessment by Commonwealth of Pennsylvania Department of Revenue | Consolidated Communications Enterprise Services Inc. (CCES)
Litigation and Contingencies
Total additional tax liability calculated by the auditors						$ 6,100
Assessment by Commonwealth of Pennsylvania Department of Revenue | Consolidated Communications of Pennsylvania Company LLC (CCPA)
Litigation and Contingencies
Total additional tax liability calculated by the auditors						$ 7,400