SEGMENT INFORMATION - Schedule of Industry Segment Results (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenue from contracts with customers	$ 275,100	$ 356,982
Earnings (Loss) Before Income Tax	4,383	19,453
Segment Assets	2,653,468	2,767,041	$ 2,693,802
Depreciation, Depletion and Amortization	54,943	50,724
Capital Expenditures	27,178	34,171
Coal Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	255,452	332,502
Terminal Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	16,501	17,818
Freight Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	3,147	6,662
PAMC
Segment Reporting Information [Line Items]
Revenue from contracts with customers	258,599	339,164
Earnings (Loss) Before Income Tax	10,875	64,698
Segment Assets	1,949,655	1,992,549
Depreciation, Depletion and Amortization	48,418	44,868
Capital Expenditures	20,692	32,372
PAMC \| Coal Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	255,452	332,502
PAMC \| Terminal Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	0	0
PAMC \| Freight Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	3,147	6,662
Other
Segment Reporting Information [Line Items]
Revenue from contracts with customers	16,501	17,818
Earnings (Loss) Before Income Tax	(6,492)	(45,245)
Segment Assets	703,813	774,492
Depreciation, Depletion and Amortization	6,525	5,856
Capital Expenditures	6,486	1,799
Other \| Coal Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	0	0
Other \| Terminal Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	16,501	17,818
Other \| Freight Revenue
Segment Reporting Information [Line Items]
Revenue from contracts with customers	$ 0	$ 0

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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