EMPLOYEE BENEFIT PLANS - Fair Value of Plan Assets (Details) - Postretirement Benefit Plans - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 8,582	$ 9,066	$ 10,369
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,582	9,066
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		10
Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		10
Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
United States equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165	180
United States equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165	180
United States equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Global equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,673	2,158
Global equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,673	2,158
Global equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,224	6,718
Fixed income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,224	6,718
Fixed income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	$ 0
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	520
Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	520
Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0