Note 1 - Summary of Significant Accounting Policies - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Total carrying amount of long-term debt	$ 29,704	$ 30,713
Estimated fair value of long-term debt	31,430	32,943
Fair Value, Recurring [Member]
Assets, fair value	4,840	5,015
Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value	4,840	5,015
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Assets, fair value	4,840	5,015
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value	$ 4,840	$ 5,015