Note 9 - Stock-based Compensation Plans and Warrants (Details Textual) - USD ($)			1 Months Ended	6 Months Ended	12 Months Ended			24 Months Ended
	Jul. 10, 2019	Dec. 18, 2009	Jan. 31, 2020	Jun. 30, 2020	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2020		Dec. 31, 2018
Share-based Payment Arrangement, Expense					$ 2,096,000		$ 562,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)					115,000	[1]	492,500	115,000	[1]	492,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)					0		0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					0		0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)					$ 12.17		$ 11.66	$ 12.17		$ 11.66
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)					253,654		49,228
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)					$ 12.51			12.51
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)					$ 9.88			$ 9.88
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense					$ 0		$ 0
Two Thousand Nine Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)		850,000
Two Thousand Nine Equity Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)		10 years
Two Thousand Nine Equity Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Month)		24 months
Two Thousand Nineteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	1,200,000				1,200,000			1,200,000
Two Thousand Nineteen Equity Incentive Plan [Member] | Outside Director [Member] | Accrues Yearly [Member]
Salary and Wage, Officer, Excluding Cost of Good and Service Sold	$ 50,000
Share-based Payment Arrangement, Expense	25,000
Two Thousand Nineteen Equity Incentive Plan [Member] | Outside Director [Member] | Accrues Quarterly [Member]
Salary and Wage, Officer, Excluding Cost of Good and Service Sold	12,500
Share-based Payment Arrangement, Expense	$ 6,250
Two Thousand Nineteen Equity Incentive Plan [Member] | Directors, Consultants and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)								269,563
Two Thousand Nineteen Equity Incentive Plan [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)				19,279				269,563
Two Thousand Nineteen Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 240,000			$ 240,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year
Two Thousand Nineteen Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)			150,000

[1] Exercise prices vary from $9.88 to $12.51, and expiration dates vary from April 2021 to December 2021.