Note 7 - Long-term Debt (Details Textual)	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Letters of Credit Outstanding, Amount	$ 310,000	$ 310,000
Texas Real Estate Agreement [Member]
Debt Instrument, Number of Installment Payments	120
Debt Instrument, Interest Rate, Stated Percentage	3.02%
Line of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 60,000,000.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Average Daily Borrowings Amount Unused Fee Trigger	$ 18,000,000.0
Ratio of Indebtedness to Net Capital	4
Line of Credit Facility, Outstanding Advances	$ 400,000	18,600,000
Letters of Credit Outstanding, Amount	300,000	$ 300,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 59,600,000
Line of Credit [Member] | Equipment Financing [Member]
Long-term Debt, Weighted Average Interest Rate, at Point in Time	2.81%
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%
Line of Credit Facility, Interest Rate at Period End	1.75%
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate	0.50%