Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (loss)	$ (3,035)	$ 290	$ (5,856)	$ (1,739)
Adjustments to reconcile net (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization			11,104	11,307
Accretion on asset retirement obligations			639	948	$ 1,493
Amortization of advance royalties			378	567
Amortization of debt issuance costs			815	670
Amortization of common unit warrants			211
Reduction of deferred revenue			(189)
Equity in net loss/(income) of unconsolidated affiliates		(40)		(36)
Loss on retirement of advance royalties			108	140
(Gain) on sale/disposal of assets-net			64	43
(Gain) on sale of Mammoth shares			(6,498)
Equity based compensation			230	260
Changes in assets and liabilities:
Accounts receivable			5,148	(5,932)
Inventories			(3,001)	(2,421)
Advance royalties			(845)	(855)
Prepaid expenses and other assets			(1,480)	(1,359)
Accounts payable			4,163	2,227
Accrued expenses and other liabilities			1,816	3,497
Asset retirement obligations			(158)	(34)
Net cash provided by operating activities			6,649	7,283
CASH FLOWS FROM INVESTING ACTIVITIES:
Additions to property, plant, and equipment			(16,000)	(10,612)
Proceeds from sales of property, plant, and equipment			4,014	406
Proceeds from business disposal				890
Proceeds from sale of Mammoth shares			11,887
Net cash used in investing activities			(99)	(9,316)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings on line of credit				64,750
Repayments on line of credit				(62,500)
Repayments on long-term debt			(10,222)
Proceeds from issuance of other debt			1,329
Repayments on other debt			(134)
Deposit for workers' compensation program			(5,209)
Payments on debt issuance costs			(629)	(227)
Preferred distributions paid			(6,039)
Net cash (used in)/provided by financing activities			(20,904)	2,023
NET (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH			(14,354)	(10)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH-Beginning of period			21,120	47	47
CASH, CASH EQUIVALENTS AND RESTRICTED CASH-End of period	6,766	37	6,766	37	21,120
Summary Statement of Financial Position:
Cash and cash equivalents						$ 3,114	$ 8,796	$ 37
Restricted cash						3,652	7,116
Total cash, cash equivalents and restricted cash	$ 6,766	$ 37	$ 6,766	$ 37	$ 21,120	$ 6,766	$ 21,120	$ 37