LONG-TERM DEBT - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Nov. 30, 2017
Debt Instrument [Line Items]
Long-term debt, net	$ 648,614	$ 685,855
Less: Unamortized Debt Issuance Costs	8,966	10,323
Less amounts due in one year	43,687	32,053
Long-Term Debt	604,927	653,802
Current portion of finance lease obligations	23,754	18,219
Loans Payable \| Term Loan B
Debt Instrument [Line Items]
Long-term debt, net	271,125	271,751
Long term debt, gross	272,250	272,938
Unamortized discount	$ 1,125	$ 1,187
Weighted average interest rate	5.49%	6.30%
Loans Payable \| MEDCO Revenue Bonds in Series due September 2025 at 5.75%
Debt Instrument [Line Items]
Long term debt, gross	$ 102,865	$ 102,865
Stated interest rate	5.75%
Loans Payable \| Term Loan A
Debt Instrument [Line Items]
Long term debt, gross	$ 85,000	$ 88,750
Weighted average interest rate	4.74%	5.55%
Loans Payable \| Advance Royalty Commitments (10.78% Weighted Average Interest Rate)
Debt Instrument [Line Items]
Long term debt, gross	$ 1,895	$ 1,895
Weighted average interest rate	10.78%
Senior Notes \| 11.00% Senior Secured Second Lien Notes due November 2025
Debt Instrument [Line Items]
Long term debt, gross	$ 178,452	221,628
Stated interest rate	11.00%		11.00%
Secured Debt \| Other Asset-Backed Financing Arrangements
Debt Instrument [Line Items]
Long term debt, gross	$ 18,243	$ 9,289
Weighted average interest rate	5.42%	5.07%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Present value of lessee's discounted obligation for lease payments from finance lease, classified as current.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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