Note 12 - Ramaco Coal Acquisition (Details)	Apr. 29, 2022 USD ($) a	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Asset Acquisition
Fair value of assets		$ 341,596,000	$ 227,077,000
Ramaco Coal Asset Acquisition
Asset Acquisition
Purchase price	$ 65,000,000
Initial payment	10,000,000
Deferred purchase price payable due in remainder of 2022	55,000,000
Quarterly Installment amount in remainder of 2022	5,000,000
Quarterly Installment amount in remainder of 2023	$ 10,000,000
Interest rate (as a percent)	9.00%
Area of thermo coal deposit Wyoming | a	16,000
Upfront payment receivable on royalty	$ 2,000,000
Minimum quarterly royalty payment receivable	125,000
Fair value of acquisition	3,700,000
Reduction in purchase price payable	1,600,000
Gain on sale of mineral rights	2,100,000
Consideration paid	68,300,000
Closing cost on asset acquisition	1,600,000
Relinquishment cost on prepaid royalties	1,600,000
Amount paid to a mineral owner as part of the acquisition	100,000
Ramaco Coal Asset Acquisition | Mining property and mineral rights
Asset Acquisition
Fair value of assets	65,100,000
Ramaco Coal Asset Acquisition | Building
Asset Acquisition
Fair value of assets	2,600,000
Ramaco Coal Asset Acquisition | Equipment
Asset Acquisition
Fair value of assets	$ 600,000