Note 1 - Summary of Significant Accounting Policies - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Total carrying amount of long-term debt	$ 30,713	$ 34,281
Estimated fair value of long-term debt	32,943	35,205
Fair Value, Recurring [Member]
Assets, fair value	5,015	3,662
Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value	5,015	3,662
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Assets, fair value	5,015	3,662
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value	$ 5,015	$ 3,662