PENSION PLAN AND OTHER BENEFIT PLANS - Amounts Recognized, Assumptions Used, Target and Actual Allocation, Fair Value, Estimated Future Benefit Payments, and Other Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss): [Abstract]
Net actuarial (gain) loss	$ (1,001)	$ (5,369)	$ 2,052
Recognized actuarial loss	(413)	(1,595)	(1,484)
Prior service credit	0	1,101	0
Amortization of prior service benefit	(220)	(427)	(90)
Total before tax effect	1,194	7,638	$ (658)
Pension Plan
Amount recognized in accumulated other comprehensive income [Abstract]
Net actuarial loss	9,356	10,788
Prior service cost	0	0
Total before tax effects	9,356	10,788
Accumulated benefit obligation	$ 42,200	$ 39,800
Principal actuarial assumptions used in determining projected benefit obligation [Abstract]
Discount rate	3.74%	4.16%	4.39%
Assumed rate of future compensation increase			5.00%
Net periodic benefit cost [Abstract]
Service cost	$ 0	$ 1,047	$ 1,231
Interest cost	1,646	1,883	1,806
Expected return on plan assets	(3,144)	(3,019)	(3,287)
Recognized actuarial loss	267	1,549	1,414
Amortization of prior service cost	0	7	7
Net periodic cost (benefit)	(1,231)	1,467	1,171
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss): [Abstract]
Net actuarial (gain) loss	(1,165)	(5,526)	1,888
Recognized actuarial loss	(267)	(1,549)	(1,414)
Amortization of prior service benefit	0	(7)	(7)
Total before tax effect	(1,432)	(7,082)	467
Total recognized in net (benefit) cost and other comprehensive income (loss) (before tax effect)	$ (2,663)	$ (5,615)	$ 1,638
Unrecognized net gain or loss increase threshold percentage for amortization of obligation (in hundredths)	10.00%
Amounts expected to be recognized in net periodic cost during next fiscal year [Abstract]
Loss recognition	$ 174
Prior service cost recognition	$ 0
Weighted-average assumptions for net periodic cost [Abstract]
Discount rate	4.16%	4.39%	4.09%
Expected long-term rate of return on assets	7.75%	7.75%	7.75%
Assumed rate of future compensation increase		5.00%	5.00%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	100.00%	100.00%
Expected long-term rate of return on assets	7.75%	7.75%	7.75%
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	$ 46,672	$ 41,560	$ 39,951
Estimated benefit payments for each of next five years and aggregate amount expected to be paid [Abstract]
2018	2,200
2019	2,244
2020	2,270
2021	2,301
2022	2,326
2023-2027	$ 11,829
Pension Plan | Minimum
Effect of a 1% decrease in health care trend rate on:
Evaluation period of expected long-term return on plan assets	3 years
Pension Plan | Maximum
Effect of a 1% decrease in health care trend rate on:
Evaluation period of expected long-term return on plan assets	5 years
Pension Plan | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	$ 46,672	41,560
Pension Plan | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	42,184	36,823
Pension Plan | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	4,488	4,737
Pension Plan | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Equity Securities - U.S. Companies | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	20,865	19,972
Pension Plan | Equity Securities - U.S. Companies | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	20,865	19,972
Pension Plan | Equity Securities - U.S. Companies | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Equity Securities - U.S. Companies | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Equity Securities - International Companies | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	847
Pension Plan | Equity Securities - International Companies | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	847
Pension Plan | Equity Securities - International Companies | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Equity Securities - International Companies | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | U.S. Treasuries/Government Bonds | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	2,217	2,218
Pension Plan | U.S. Treasuries/Government Bonds | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | U.S. Treasuries/Government Bonds | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	2,217	2,218
Pension Plan | U.S. Treasuries/Government Bonds | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Corporate bonds and notes | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	2,271	2,519
Pension Plan | Corporate bonds and notes | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Corporate bonds and notes | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	2,271	2,519
Pension Plan | Corporate bonds and notes | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Mutual Funds | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	19,253	14,680
Pension Plan | Mutual Funds | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	19,253	14,680
Pension Plan | Mutual Funds | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Mutual Funds | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	$ 0	$ 0
Pension Plan | Large-Cap Domestic Equities
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	10.30%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	40.00%	57.00%
Expected long-term rate of return on assets	10.30%
Pension Plan | Large-Cap Domestic Equities | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	30.00%
Pension Plan | Large-Cap Domestic Equities | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	60.00%
Pension Plan | Mid-Cap Domestic Equities
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	10.60%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	6.00%	5.00%
Expected long-term rate of return on assets	10.60%
Pension Plan | Mid-Cap Domestic Equities | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	0.00%
Pension Plan | Mid-Cap Domestic Equities | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	20.00%
Pension Plan | Small-Cap Domestic Equities
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	10.80%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	7.00%	2.00%
Expected long-term rate of return on assets	10.80%
Pension Plan | Small-Cap Domestic Equities | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	0.00%
Pension Plan | Small-Cap Domestic Equities | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	15.00%
Pension Plan | International Equities
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	10.30%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	13.00%	7.00%
Expected long-term rate of return on assets	10.30%
Pension Plan | International Equities | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	0.00%
Pension Plan | International Equities | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	25.00%
Pension Plan | Intermediate Fixed Income
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	4.70%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	29.00%	26.00%
Expected long-term rate of return on assets	4.70%
Pension Plan | Intermediate Fixed Income | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	20.00%
Pension Plan | Intermediate Fixed Income | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	50.00%
Pension Plan | Alternative Assets
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	7.50%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	0.00%	0.00%
Expected long-term rate of return on assets	7.50%
Pension Plan | Alternative Assets | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	0.00%
Pension Plan | Alternative Assets | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	10.00%
Pension Plan | Cash
Weighted-average assumptions for net periodic cost [Abstract]
Expected long-term rate of return on assets	2.50%
Target allocations of plan assets [Abstract]
Percentage of plan assets (in hundredths)	5.00%	3.00%
Expected long-term rate of return on assets	2.50%
Pension Plan | Cash | Minimum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	0.00%
Pension Plan | Cash | Maximum
Target allocations of plan assets [Abstract]
Target allocation, minimum (in hundredths)	20.00%
Pension Plan | Cash | Carrying Value
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	$ 2,066	$ 1,324
Pension Plan | Cash | Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	2,066	1,324
Pension Plan | Cash | Fair Value | Significant Other Observable Inputs (Level 2)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Pension Plan | Cash | Fair Value | Significant Unobservable Inputs (Level 3)
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	0	0
Defined Benefit Health Care Plan
Amount recognized in accumulated other comprehensive income [Abstract]
Net actuarial loss	592	636
Prior service cost	(881)	(1,101)
Total before tax effects	$ (289)	$ (465)
Principal actuarial assumptions used in determining projected benefit obligation [Abstract]
Discount rate	3.74%	4.16%	4.39%
Net periodic benefit cost [Abstract]
Service cost	$ 0	$ 43	$ 46
Interest cost	20	66	70
Recognized actuarial loss	143	20	20
Recognized prior service benefit due to curtailments	0	(337)	0
Amortization of prior service cost	(220)	(97)	(97)
Net periodic cost (benefit)	(57)	(305)	39
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss): [Abstract]
Net actuarial (gain) loss	(98)	(139)	(216)
Recognized actuarial loss	143	20	20
Prior service credit	0	(1,101)	0
Amortization of prior service benefit	220	434	97
Total before tax effect	175	(548)	293
Total recognized in net (benefit) cost and other comprehensive income (loss) (before tax effect)	$ 118	$ (853)	$ 332
Average future working lifetime of active participants	5 years
Amounts expected to be recognized in net periodic cost during next fiscal year [Abstract]
Loss recognition	$ 110
Prior service cost recognition	$ (220)
Weighted-average assumptions for net periodic cost [Abstract]
Discount rate	4.16%	4.39%	4.09%
Health care cost trend: Initial	6.50%	6.50%	7.00%
Health care cost trend: Ultimate	5.00%	5.00%	5.00%
Health care cost trend rate assumed for net periodic benefit (cost), next fiscal year	6.50%	7.00%	7.00%
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	$ 0	$ 0	$ 0
Estimated benefit payments for each of next five years and aggregate amount expected to be paid [Abstract]
2018	139
2019	111
2020	59
2021	38
2022	28
2023-2027	77
Effect of a 1% increase in health care trend rate on:
Benefit obligation	5	2	3
Total service and interest cost	0	0	0
Effect of a 1% decrease in health care trend rate on:
Benefit obligation	(6)	(3)	(3)
Total service and interest cost	0	0	$ 0
Estimated employer contributions in next fiscal year	139
Executive Supplemental Pension Plan
Amount recognized in accumulated other comprehensive income [Abstract]
Net actuarial loss	228	165
Prior service cost	0	0
Total before tax effects	228	$ 165
Accumulated benefit obligation	$ 1,300
Principal actuarial assumptions used in determining projected benefit obligation [Abstract]
Discount rate	3.74%	4.16%	4.39%
Assumed rate of future compensation increase			5.00%
Net periodic benefit cost [Abstract]
Service cost	$ 0	$ 43	$ 44
Interest cost	50	51	49
Recognized actuarial loss	3	26	50
Net periodic cost (benefit)	53	120	143
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss): [Abstract]
Net actuarial (gain) loss	(66)	(18)	52
Recognized actuarial loss	3	26	50
Total before tax effect	63	(8)	(102)
Total recognized in net (benefit) cost and other comprehensive income (loss) (before tax effect)	$ 116	$ 112	$ 41
Unrecognized net gain or loss increase threshold percentage for amortization of obligation (in hundredths)	10.00%
Amounts expected to be recognized in net periodic cost during next fiscal year [Abstract]
Loss recognition	$ 7
Prior service cost recognition	$ 0
Weighted-average assumptions for net periodic cost [Abstract]
Discount rate	4.16%	4.39%	4.09%
Assumed rate of future compensation increase			5.00%
Fair value plan assets by asset class [Abstract]
Fair value of plan assets	$ 0	$ 0	$ 0
Estimated benefit payments for each of next five years and aggregate amount expected to be paid [Abstract]
2018	109
2019	107
2020	106
2021	104
2022	101
2023-2027	456
Effect of a 1% decrease in health care trend rate on:
Estimated employer contributions in next fiscal year	$ 110