CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net Income (Loss)	$ 13,631	$ 11,783	$ (22,567)
Depreciation, depletion, and amortization	34,121	32,215	33,209
Amortization of intangible assets	214	0
Accretion of asset retirement obligation	1,793	1,668	1,558
Amortization of deferred financing costs	303	732	1,778
Stock-based compensation	4,281	4,179	3,622
Allowance for doubtful accounts	75	100	865
(Gain) loss on disposal of assets	345	(87)	1,830
Lower of cost or net realizable value inventory adjustments	1,810	1,711	6,379
Other	(34)	(4)	1,073
Changes in operating assets and liabilities:
Trade accounts receivable, net	1,337	(7,484)	(6,870)
Other receivables, net	(650)	165	(270)
Refundable income taxes		2,663	(1,284)
Inventory, net	(11,525)	(67)	(1,263)
Other current assets	(1,019)	1,762	(3,207)
Accounts payable, accrued liabilities and accrued employee compensation and benefits	2,280	1,740	1,738
Income taxes payable	(865)	914
Operating lease liabilities	(2,090)
Other liabilities	5,374	12,247	102
Net cash provided by operating activities	49,381	64,237	16,693
Cash Flows from Investing Activities:
Additions to property, plant, equipment, and mineral properties	(63,836)	(16,891)	(13,505)
Additions to intangible Assets	(16,873)
Proceeds from sale of property, plant, equipment, and mineral properties	68	110	5,651
Net cash used in investing activities	(80,641)	(16,781)	(7,854)
Cash Flows from Financing Activities:
Issuance of common stock, net of transaction expense			59,130
Repayments of long-term debt		(10,000)	(75,000)
Debt prepayment costs		(402)	(3,001)
Proceeds from from short-term borrowings on credit facility	30,317	13,500	22,000
Repayments of short-term borrowings on credit facility	(10,500)	(17,400)	(18,100)
Capitalized debt costs	(503)	(210)	(129)
Employee tax withholding paid for restricted stock upon vesting	(540)	(903)	(781)
Proceeds from exercise of stock options	21	114	121
Net cash provided by (used in) financing activities	18,795	(15,301)	(15,760)
Net Change in Cash, Cash Equivalents, and Restricted Cash	(12,465)	32,155	(6,921)
Cash, Cash Equivalents, and Restricted Cash, beginning of period	33,704	1,549	8,470
Cash, Cash Equivalents, and Restricted Cash, end of period	21,239	33,704	1,549
Supplemental disclosure of cash flow information
Interest, net of $0.2 million of capitalized interest in 2019, and $0.1 million in both 2018 and 2017	2,733	3,470	11,639
Income taxes	942	(3,469)	(1,499)
Accrued purchases for property, plant, equipment, mineral properties, and development costs	$ 5,021	$ 1,082	$ 4,068