Note 3 - Summary of Significant Accounting Policies (Details Textual) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accounts Receivable, Allowance for Credit Loss, Current	$ 213,000		$ 213,000		$ 322,000
Accounts Receivable, Credit Loss Expense (Reversal)	35,000	$ 2,000	3,000	$ 298,000
Inventory Write-down	0	0	0	0
Interest Costs Capitalized	0	0	0	0
Impairment of Long-Lived Assets Held-for-use	0		0
Impairment of Long-Lived Assets to be Disposed of	0	0	0	0
Goodwill and Intangible Asset Impairment, Total	0	$ 0	0	$ 0
Employee Retention Tax Credit, Maximum Amount Per Employee Per Quarter			7,000
Employee Retention Tax Credit	$ 1,000,000.0		$ 1,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Options and Warrants, Outstanding, Number (in shares)	1,377,516	173,166	1,377,516	173,166
Share-based Compensation Arrangement by Share-based Payment Award, Options and Warrants, Outstanding, Aggregate Intrinsic Value	$ 0	$ 0	$ 0	$ 0
Payments of Dividends, Total	$ 0
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Open Tax Year	2017 2018 2019 2020
State and Local Jurisdiction [Member]
Open Tax Year	2016 2017 2018 2019 2020
Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)	5 years
Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)	30 years