Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net income (loss)	$ (4,907)	$ 24,934	$ 25,074
Adjustments to reconcile net income (loss) to net cash from operating activities:
Accretion of asset retirement obligations	570	511	494
Depreciation and amortization	20,912	19,521	12,423
Amortization of debt issuance costs	58	58	569
Stock-based compensation	4,140	4,060	2,638
Other income - PPP Loan	(8,444)
Deferred income taxes	(3,503)	5,156	109
Changes in operating assets and liabilities:
Accounts receivable	(1,043)	(8,527)	(3,563)
Prepaid expenses and other current assets	986	723	(629)
Inventories	3,314	(1,076)	(4,127)
Other assets and liabilities	(1,270)	689	(835)
Accounts payable	2,753	(7,313)	(1,521)
Accrued expenses	(254)	3,646	5,551
Net cash from operating activities	13,312	42,382	36,183
Cash flow from investing activities:
Purchases of property, plant and equipment	(24,753)	(45,722)	(48,137)
Proceeds from maturities of investment securities			5,200
Net cash from investing activities	(24,753)	(45,722)	(42,937)
Cash flows from financing activities
Proceeds from PPP Loan	8,444
Proceeds from borrowings	50,043	73,750	28,424
Proceeds from notes payable - related party			3,000
Payments of debt issuance cost			(569)
Repayment of borrowings	(45,598)	(70,335)	(18,950)
Repayment of notes payable - related party			(3,000)
Repayments of financed insurance payable	(1,382)	(570)	(989)
Restricted stock surrendered for withholding taxes payable	(221)	(20)
Net cash from financing activities	11,286	2,825	7,916
Net change in cash and cash equivalents and restricted cash	(155)	(515)	1,162
Cash and cash equivalents and restricted cash, beginning of period	6,865	7,380	6,218
Cash and cash equivalents and restricted cash, end of period	6,710	6,865	7,380
Supplemental cash flow information:
Cash paid for interest	1,095	999	826
Cash paid for taxes	19
Non-cash investing and financing activities:
Capital expenditures included in accounts payable and accrued expenses	1,228	2,902	1,319
Financed insurance	1,588	939	$ 1,276
Additional asset retirement obligations incurred	$ 86	$ 516