EMPLOYEE BENEFIT PLANS - Plan Asset Fair Value (Details) - Qualified Plan - Qualified Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair value hierarchy of Plan's assets
Total investments	$ 260,926	$ 201,843
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	260,926	201,843
Fair value of plan assets at end of year	253,955	260,926
Cash
Fair value hierarchy of Plan's assets
Total investments	39,897	39,897
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	39,897
Fair value of plan assets at end of year	1,225	39,897
Equity securities
Fair value hierarchy of Plan's assets
Total investments	146,143	146,143
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	146,143
Fair value of plan assets at end of year	158,823	146,143
Fixed income
Fair value hierarchy of Plan's assets
Total investments	15,200
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year	15,200
Group deposit administration annuity contract
Fair value hierarchy of Plan's assets
Total investments	74,886	74,886
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	74,886
Fair value of plan assets at end of year	78,707	74,886
Level 1
Fair value hierarchy of Plan's assets
Total investments	186,040	186,040
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	186,040
Fair value of plan assets at end of year	175,248	186,040
Level 1 | Cash
Fair value hierarchy of Plan's assets
Total investments	39,897	39,897
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	39,897
Fair value of plan assets at end of year	1,225	39,897
Level 1 | Equity securities
Fair value hierarchy of Plan's assets
Total investments	146,143	146,143
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	146,143
Fair value of plan assets at end of year	158,823	146,143
Level 1 | Fixed income
Fair value hierarchy of Plan's assets
Total investments	15,200
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year	15,200
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
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
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
Level 2 | Equity securities
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
Level 2 | Fixed income
Fair value hierarchy of Plan's assets
Total investments	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year	0
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
Level 3
Fair value hierarchy of Plan's assets
Total investments	74,886	71,226
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	74,886	71,226
Interest income	3,821	3,660
Transfers from collective short-term investments fund	0	0
Transfers to collective short-term investments fund	0	0
Fair value of plan assets at end of year	78,707	74,886
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
Level 3 | Equity securities
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
Level 3 | Fixed income
Fair value hierarchy of Plan's assets
Total investments	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year	0
Level 3 | Group deposit administration annuity contract
Fair value hierarchy of Plan's assets
Total investments	74,886	74,886
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	74,886
Fair value of plan assets at end of year	$ 78,707	$ 74,886