Note 9 - Commitments and Contingencies (Details Textual) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Loss Contingency Accrual, Provision	$ 1,150,000
Accounts Receivable, Credit Loss Expense (Reversal)	$ 499,000	$ (1,026,000)	$ 421,000
Standard Product Warranty Accrual, Period Increase (Decrease), Total		0	0
Standard Product Warranty Accrual, Ending Balance		159,000	159,000
Performance Guarantees [Member]
Debt Instrument, Face Amount		1,134
Standby Letters of Credit [Member] | Cash Collateral Security Agreement [Member]
Letters of Credit Outstanding, Amount		1,873,000
Receivables [Member]
Loss Contingency, Receivable, Ending Balance		2,589,000
Failure of Equipment to Be Remedied Under Warranty Provision [Member]
Loss Contingency Accrual, Ending Balance		176,000
Failure of Equipment to Be Remedied Under Warranty Provision [Member] | Other Accrued Liabilities [Member]
Loss Contingency Accrual, Ending Balance		$ 176,000	$ 146,000