Note 7 - Stock-based Awards - Summary of Shares Granted Under the 2006 Incentive Plan (Details) - $ / shares			12 Months Ended
		Nov. 11, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		40,000	40,000
Fair value per share (in dollars per share)			$ 4.14
December 16, 2020 [Member] | Stock Unit Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			5,000
Fair value per share (in dollars per share)	[1]		$ 4.71
November 11, 2020 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			40,000
Fair value per share (in dollars per share)	[1]		$ 1.13
November 11, 2020 [Member] | Stock Unit Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			190,000
Fair value per share (in dollars per share)	[1]		$ 4.07
May 3, 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			192,000
Fair value per share (in dollars per share)	[1]		$ 2.99
May 3, 2019 [Member] | Stock Unit Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			18,000
Fair value per share (in dollars per share)	[1]		$ 10.60
July 24, 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			2,000
Fair value per share (in dollars per share)	[1]		$ 5.49
May 3, 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			117
Fair value per share (in dollars per share)			$ 5.69
May 3, 2018 [Member] | Stock Unit Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)			6,000
Fair value per share (in dollars per share)	[1]		$ 21.04

[1] The fair value for the SUA's is the closing price of the Company's stock on that date. The fair value for options represents the fair value calculated using the Black-Scholes model. Options have contractual lives of 10 years. The options granted on May 3, 2018 have a fair value of $5.69 per share based on the $21.04 grant date and exercise prices and assuming 6.25 and 5.75 year estimated terms, 38% volatility, 3.4% interest rate and a 4.2% dividend yield rate. The options granted on July 24, 2018 have a fair value of $5.49 per share based on the $19.83 grant date and exercise prices and assuming a 6.25 year estimated term, 39% volatility, 3.4% interest rate and a 4.1% dividend yield rate. The options granted on May 3, 2019 have a fair value of $2.99 per share based on the $10.60 grant date and exercise prices and assuming 6.25 and 5.75 year estimated terms, 41% volatility, 2.4% interest rate and a 3.9% dividend yield rate. The options granted on November 11, 2020 have a fair value of $1.13 per share based on the $4.07 grant date and exercise prices and assuming 6.25 and 5.75 year estimated terms, 45% volatility, 0.9% interest rate and a 4.0% dividend yield rate. For options granted during fiscal years ended December 31, 2020, 2019, and 2018, the weighted average grant date fair values were $3.47, $3.40 and $2.49, respectively. For SUAs granted during fiscal years ended December 31, 2020, 2019, and 2018, the weighted average grant date fair values were $4.89, $12.01 and $14.42, respectively.