Note 7 - Long-term Debt (Details Textual)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Letters of Credit Outstanding, Amount	$ 430,000	$ 700,000
Line of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 60,000,000
Line of Credit Facility, Interest Rate at Period End	2.96%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.25%
Average Daily Borrowings Amount Unused Fee Trigger	$ 18,000,000
Ratio of Indebtedness to Net Capital		4
Line of Credit Facility, Outstanding Advances	17,400,000	$ 10,900,000
Letters of Credit Outstanding, Amount	400,000	$ 700,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 42,600,000
Line of Credit [Member] | Equipment Financing [Member]
Long-term Debt, Weighted Average Interest Rate, at Point in Time	3.65%
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	1.25%