Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	[1]	May 31, 2017	Nov. 30, 2010
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)				11,300
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)		45,326		21,110
Letters of Credit Outstanding, Amount		$ 500		$ 500
Accounts Receivable, Allowance for Credit Loss, Current		493		493		$ 335
Proceeds from Sale of Property, Plant, and Equipment, Total		6,019		6,019
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property		3,821		3,821
Amortization of Intangible Assets, Total		47		145
Impairment of Long-Lived Assets to be Disposed of		$ 0	0	$ 0	0
Minnesota Facilities [Member]
Lessee, Operating Lease, Term of Contract (Year)		15 years		15 years
Lessee, Operating Lease, Renewal Term (Year)		5 years		5 years
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense		$ 36	35	$ 111	226
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		260		$ 260
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)				2 years 142 days
Stock Appreciation Rights (SARs) [Member]
Share-based Payment Arrangement, Expense		40	$ 0	$ 40	$ 0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 40		$ 40
Stock Incentive Plan 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)								400,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)	50,000
Equity Appreciation Rights Plan 2010 [Member] | Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)									1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)				0	137,500

[1] The balance sheet at December 31, 2019 has been derived from the audited financial statements at that date