Note 8 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Net operating loss and tax credit carryforwards	$ 24,956	$ 29,545
Joint venture and other investments	(27)	(27)
Accrued retirement benefits	3,329	3,010
Property net book value	3,357	3,300
Deferred revenue	715	697
Reserves and other	29	(10)
Total deferred tax assets	32,359	36,515
Valuation allowance	(32,359)	(36,515)
Net deferred tax assets