EMPLOYEE BENEFIT PLANS - Asset Allocation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	100.00%		100.00%
Percentage of investments for long-term growth, investment strategy mix	70.00%
Percentage of investments for near-term benefit payments, investment strategy mix	30.00%
Pension plan assets	$ 219,905		$ 194,342	$ 190,640
Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	53,724		60,568
Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	145,638		115,004
Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 20,543		$ 18,770
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	2.40%		3.50%
Pension plan assets	$ 5,432		$ 6,834
Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 5,432		$ 6,834
Common Stock
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	14.70%		20.70%
Pension plan assets	$ 32,049		$ 42,120
Common Stock | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 32,049		$ 42,120
Domestic equity - all other
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	21.80%		21.70%
Pension plan assets	$ 48,511		$ 40,178
Domestic equity - all other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	16,243		11,614
Domestic equity - all other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 32,268		$ 28,564
International equity
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	16.40%		21.00%
Pension plan assets	$ 36,156		$ 40,767
International equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			0
International equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 36,156		$ 40,767
Debt securities - core fixed income
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	35.20%		23.50%
Pension plan assets	$ 77,214		$ 45,673
Debt securities - core fixed income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets
Debt securities - core fixed income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 77,214		$ 45,673
Real estate
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	6.50%		6.40%
Pension plan assets	$ 14,074		$ 12,527
Real estate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 14,074		$ 12,527
Alternative/Opportunistic/Special
Defined Benefit Plan Disclosure [Line Items]
Percentage of plan assets	3.00%		3.20%
Pension plan assets	$ 6,469		$ 6,243
Alternative/Opportunistic/Special | Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 6,469		$ 6,243
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Target allocation
Scenario, Forecast | Cash and cash equivalents | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		0.00%
Scenario, Forecast | Cash and cash equivalents | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		5.00%
Scenario, Forecast | Common Stock | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		0.00%
Scenario, Forecast | Common Stock | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		40.00%
Scenario, Forecast | Domestic equity - all other | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		0.00%
Scenario, Forecast | Domestic equity - all other | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		40.00%
Scenario, Forecast | International equity | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		0.00%
Scenario, Forecast | International equity | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		30.00%
Scenario, Forecast | Debt securities - core fixed income | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		15.00%
Scenario, Forecast | Debt securities - core fixed income | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		50.00%
Scenario, Forecast | Real estate | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		0.00%
Scenario, Forecast | Real estate | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		20.00%
Scenario, Forecast | Alternative/Opportunistic/Special | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		0.00%
Scenario, Forecast | Alternative/Opportunistic/Special | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation		20.00%