Note 4 - Stock-based Compensation (Details Textual) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	[1]
Incentive Plan 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)		231		231
Share-based Payment Arrangement, Expense, Tax Benefit		$ 0	$ 0	$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value		$ 0		$ 0		$ 0
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		820		820
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 800		$ 800
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)				2 years 146 days

[1] Stock options had no aggregate intrinsic value as of December 31, 2019 and June 30, 2020. Intrinsic value is calculated based on the amount by which the closing market value of the Company's stock exceeded the exercise price of the underlying options, multiplied by the number of shares.