Note 12 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Net operating loss and tax credit carryforwards	$ 24,648	$ 23,980
Joint venture and other investments	(446)	(27)
Accrued retirement benefits and other compensation	1,233	1,149
Property net book value	3,002	2,960
Deferred revenue	962	1,016
Reserves and other	37	(50)
Total deferred tax assets	29,436	29,028
Valuation allowance	(29,436)	(29,028)
Net deferred tax assets	$ 0	$ 0