Note 8 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Net operating loss and tax credit carryforwards	$ 24,239	$ 25,745
Joint venture and other investments	(27)	(22)
Accrued retirement benefits	3,055	2,483
Property net book value	2,266	1,716
Deferred revenue	666	546
Stock compensation	16	13
Reserves and other	189	(115)
Total deferred tax assets	30,404	30,366
Valuation allowance	(30,404)	(30,366)
Net deferred tax assets