RETIREMENT PLANS - Benefit Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension benefits
Projected benefit obligations:
Balance at beginning of year	$ 88,772	$ 81,977
Alaska acquisition	15,399
Service cost	229	439	$ 1,709
Interest cost	2,043	2,585	3,472
Benefits and settlements paid	(4,488)	(4,791)
Actuarial (gain) loss	(1,297)	8,651
Settlement	(34)	(89)
Balance at end of year	100,624	88,772	81,977
Plan net assets:
Balance at beginning of year	89,352	83,350
Alaska acquisition	12,147
Actual return on plan assets	7,246	10,398
Company contributions		958
Benefits and settlements paid	(5,027)	(5,354)
Balance at end of year	103,718	89,352	83,350
Funded status of plan
Projected benefit obligation	100,624	88,772	81,977
Plan Net Assets	103,718	89,352	83,350
Over/ (Under) funded status of plan	3,094	580
Pension benefits | GT&T Pension Benefit
Projected benefit obligations:
Balance at beginning of year	15,609
Balance at end of year	15,663	15,609
Plan net assets:
Balance at beginning of year	15,609
Balance at end of year	15,663	15,609
Funded status of plan
Projected benefit obligation	15,663	15,609
Plan Net Assets	15,663	15,609
Pension benefits | Viya Pension Benefit
Projected benefit obligations:
Balance at beginning of year	73,163
Balance at end of year	70,173	73,163
Plan net assets:
Balance at beginning of year	73,743
Balance at end of year	75,952	73,743
Funded status of plan
Projected benefit obligation	70,173	73,163
Plan Net Assets	75,952	73,743
Over/ (Under) funded status of plan	5,779	580
Pension benefits | Alaska Pension Benefit
Projected benefit obligations:
Balance at end of year	14,788
Plan net assets:
Balance at end of year	12,103
Funded status of plan
Projected benefit obligation	14,788
Plan Net Assets	12,103
Over/ (Under) funded status of plan	(2,685)
Postretirement benefits
Projected benefit obligations:
Balance at beginning of year	5,510	4,899
Alaska acquisition	392
Service cost	143	139	126
Interest cost	127	163	182
Benefits and settlements paid	(390)	(450)
Actuarial (gain) loss	(439)	759
Balance at end of year	5,343	5,510	4,899
Plan net assets:
Company contributions	390	450
Benefits and settlements paid	(390)	(450)
Funded status of plan
Projected benefit obligation	5,343	5,510	$ 4,899
Over/ (Under) funded status of plan	(5,343)	$ (5,510)
Postretirement benefits | Viya Pension Benefit
Projected benefit obligations:
Balance at end of year	4,961
Funded status of plan
Projected benefit obligation	4,961
Over/ (Under) funded status of plan	(4,961)
Postretirement benefits | Alaska Pension Benefit
Projected benefit obligations:
Balance at end of year	382
Funded status of plan
Projected benefit obligation	382
Over/ (Under) funded status of plan	$ (382)