Supplemental Financial Information (Tables)

12 Months Ended

Dec. 31, 2020

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Schedule of Prepaid Expenses and Other Assets and Other assets

The following table summarizes the components of Prepaid expenses and other current assets and Other long-term assets, net as presented in the Consolidated Balance Sheets:

	As of December 31,
(in thousands)	2020		2019
Prepaid expenses and other current assets:
Prepaid expenses	$	1,690	$	1,708
Prepaid income taxes	1,605		4,228
Other	1,302		1,896
	$	4,597	$	7,832
Other long-term assets:
Upfront customer consideration (1)	$	7,490	$	—
Cabot receivable (1)	8,852		—
Right of use assets, operating leases, net	1,930		5,073
Spare parts, net	3,727		3,453
Mine development costs, net	4,338		7,084
Mine reclamation asset, net	1,712		2,451
Highview investment	552		552
Other long-term assets	1,388		1,718
	$	29,989	$	20,331

(1) See further discussion of Upfront Customer Consideration in Note 3 and Cabot receivable in Note 4.

Schedule of Other Liabilities

The following table details the components of Other current liabilities and Other long-term liabilities as presented in the Consolidated Balance Sheets:

	As of December 31,
(in thousands)	2020		2019
Other current liabilities:
Current portion of operating lease obligations	$	1,883	$	2,382
Accrued interest	69		213
Income and other taxes payable	1,305		678
Current portion of mine reclamation liability	9,370		—
Other current liabilities	369		1,038
	$	12,996	$	4,311
Other long-term liabilities:
Operating lease obligations, long-term	$	1,109	$	2,810
Mine reclamation liabilities	12,077		2,721
Other	287		229
	$	13,473	$	5,760

Schedule of Change in Asset Retirement Obligation

The Mine reclamation liability related to the Five Forks Mine is included in Other long-term liabilities. The Mine reclamation liability related to Marshall Mine, which was assumed in the Marshall Mine Acquisition is included in Other current liabilities and Other long-term liabilities. The Mine reclamation liabilities represent AROs. Changes in the AROs were as follows:

	As of December 31,
(in thousands)	2020		2019
Asset retirement obligations, beginning of year	$	2,721	$	624
Asset retirement obligations assumed	21,328		1,776
Accretion	543		205
Liabilities settled	(3,565)		(78)
Changes due to scope and timing of reclamation	420		194
Asset retirement obligations, end of year	21,447		2,721
Less current portion	9,370		—
Asset retirement obligations, long-term	$	12,077	$	2,721

Schedule of Statement of Operations, Supplemental Disclosures

The following table details the components of Interest expense in the Consolidated Statements of Operations:

	Years Ended December 31,
(in thousands)	2020		2019
Interest on Senior Term Loan	$	1,708	$	4,112
Debt discount and debt issuance costs	1,418		1,678
453A interest	331		1,039
Other	463		345
	$	3,920	$	7,174

The following table details the components of Other in the Consolidated Statements of Operations:

	Years Ended December 31,
(in thousands)	2020		2019
Interest income	$	127	$	261
Other	5		166
	$	132	$	427