Acquisition - Allocation (Details) - ADA Carbon Solutions, LLC - USD ($) $ in Thousands		13 Months Ended
	Dec. 07, 2018	Dec. 31, 2019
Fair value of assets acquired:
Cash	$ 3,284	$ 3,284
Receivables	6,409	6,409
Inventories	22,100	21,744
Prepaid expenses and other current assets	2,992	3,053
Spare parts	3,359	3,359
Property, plant and equipment	43,033	42,656
Mine leases and development	2,500	2,700
Mine reclamation asset	0	2,402
Intangible assets	4,000	4,100
Other assets	168	168
Amount attributable to assets acquired	87,845	89,875
Fair value of liabilities assumed:
Accounts payable	4,771	4,771
Accrued liabilities	7,354	7,608
Equipment lease liabilities	8,211	8,211
Mine reclamation liability	626	2,402
Other liabilities	437	437
Amount attributable to liabilities assumed	21,399	23,429
Net assets acquired	$ 66,446	66,446
Adjustments
Cash		0
Receivables		0
Inventories		(356)
Prepaid expenses and other current assets		61
Spare parts		0
Property, plant and equipment		(377)
Mine leases and development		200
Mine reclamation asset		2,402
Intangible assets		100
Other assets		0
Amount attributable to assets acquired		2,030
Accounts payable		0
Accrued liabilities		254
Equipment lease liabilities		0
Mine reclamation liability		1,776
Other liabilities		0
Amount attributable to liabilities assumed		2,030
Net assets acquired		0
Customer relationships
Fair value of assets acquired:
Intangible assets		2,200
Adjustments
Weighted Average Useful Life (years)	5 years
Developed technology
Fair value of assets acquired:
Intangible assets		1,600
Adjustments
Weighted Average Useful Life (years)	5 years
Trade name
Fair value of assets acquired:
Intangible assets		$ 300
Adjustments
Weighted Average Useful Life (years)	2 years