Note 10 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Net operating loss and tax credit carryforwards	$ 23,980	$ 25,132
Joint venture and other investments	(27)	(27)
Accrued retirement benefits	1,149	2,545
Property net book value	2,960	2,862
Deferred revenue	1,016	1,083
Reserves and other	(50)	(5)
Total deferred tax assets	29,028	31,590
Valuation allowance	(29,028)	(31,590)
Net deferred tax assets	$ 0	$ 0