EMPLOYEE BENEFIT PLANS - Plan Asset Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Level 3
Fair value hierarchy of Plan's assets
Amount transferred from level 3 to level 1	$ 7,500
Qualified Plan | Qualified Pension Plan
Fair value hierarchy of Plan's assets
Total investments	253,955	$ 253,955
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	253,955	260,926
Fair value of plan assets at end of year	304,822	253,955
Qualified Plan | Qualified Pension Plan | Cash
Fair value hierarchy of Plan's assets
Total investments	1,225	1,225
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	1,225
Fair value of plan assets at end of year	3,713	1,225
Qualified Plan | Qualified Pension Plan | Return-Seeking
Fair value hierarchy of Plan's assets
Total investments	158,823	158,823
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	158,823
Fair value of plan assets at end of year	189,362	158,823
Qualified Plan | Qualified Pension Plan | Fixed income
Fair value hierarchy of Plan's assets
Total investments	15,200	15,200
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	15,200
Fair value of plan assets at end of year	36,695	15,200
Qualified Plan | Qualified Pension Plan | Group deposit administration annuity contract
Fair value hierarchy of Plan's assets
Total investments	78,707	78,707
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	78,707
Fair value of plan assets at end of year	75,052	78,707
Qualified Plan | Qualified Pension Plan | Level 1
Fair value hierarchy of Plan's assets
Total investments	175,248	175,248
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	175,248
Fair value of plan assets at end of year	229,770	175,248
Qualified Plan | Qualified Pension Plan | Level 1 | Cash
Fair value hierarchy of Plan's assets
Total investments	1,225	1,225
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	1,225
Fair value of plan assets at end of year	3,713	1,225
Qualified Plan | Qualified Pension Plan | Level 1 | Return-Seeking
Fair value hierarchy of Plan's assets
Total investments	158,823	158,823
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	158,823
Fair value of plan assets at end of year	189,362	158,823
Qualified Plan | Qualified Pension Plan | Level 1 | Fixed income
Fair value hierarchy of Plan's assets
Total investments	15,200	15,200
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	15,200
Fair value of plan assets at end of year	36,695	15,200
Qualified Plan | Qualified Pension Plan | Level 1 | Group deposit administration annuity contract
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 2
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 2 | Cash
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 2 | Return-Seeking
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 2 | Fixed income
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 2 | Group deposit administration annuity contract
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 3
Fair value hierarchy of Plan's assets
Total investments	78,707	78,707
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	78,707	74,886
Interest income	3,845	3,821
Transfers from collective short-term investments fund	0	0
Transfers to collective short-term investments fund	(7,500)	0
Fair value of plan assets at end of year	75,052	78,707
Qualified Plan | Qualified Pension Plan | Level 3 | Cash
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 3 | Return-Seeking
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 3 | Fixed income
Fair value hierarchy of Plan's assets
Total investments	0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	0
Fair value of plan assets at end of year	0	0
Qualified Plan | Qualified Pension Plan | Level 3 | Group deposit administration annuity contract
Fair value hierarchy of Plan's assets
Total investments	78,707	78,707
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	78,707
Fair value of plan assets at end of year	$ 75,052	$ 78,707