Note 8 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Net operating loss and tax credit carryforwards	$ 25,132	$ 24,956
Joint venture and other investments	(27)	(27)
Accrued retirement benefits	2,545	3,329
Property net book value	2,862	3,357
Deferred revenue	1,083	715
Reserves and other	(5)	29
Total deferred tax assets	31,590	32,359
Valuation allowance	(31,590)	(32,359)
Net deferred tax assets	$ 0	$ 0