Note 9 - Debt (Details Textual) - USD ($)			1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 05, 2021	Apr. 15, 2021	Apr. 30, 2020	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Long-term Debt, Total				$ 66,825,000	$ 66,825,000	$ 1,254,000
Letter of Credit [Member]
Debt Instrument, Face Amount		$ 71,200,000
The 2021 Bonds [Member]
Debt Instrument, Face Amount		$ 68,155,000
Debt Instrument, Interest Rate, Stated Percentage		1.50%
Debt Instrument, Unamortized Premium, Total		$ 800,000		700,000	700,000
Debt Issuance Costs, Net, Total		3,000,000.0		2,600,000	2,600,000
Amortization of Debt Discount (Premium)				100,000	100,000
Amortization of Debt Issuance Costs				$ 300,000	$ 500,000
SBA Loans [Member]
Proceeds from Issuance of Long-term Debt, Total			$ 1,000,000.0
Debt Instrument, Decrease, Forgiveness		500,000
SBA Loans [Member] | Agri-Energy [Member]
Debt Instrument, Decrease, Forgiveness		100,000
Long-term Debt, Total		$ 400,000
Debt Instrument, Periodic Payment, Total	$ 8,000