Note 8 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Net operating loss and tax credit carryforwards	$ 29,545	$ 24,239
Joint venture and other investments	(27)	(27)
Accrued retirement benefits	3,010	3,055
Property net book value	3,300	2,266
Deferred revenue	697	666
Stock compensation		16
Reserves and other	(10)	189
Total deferred tax assets	36,515	30,404
Valuation allowance	(36,515)	(30,404)
Net deferred tax assets