Note 8 - Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Net operating loss and tax credit carryforwards	$ 25,745	$ 38,915
Joint venture and other investments	(22)	18
Accrued retirement benefits	2,483	3,924
Property net book value	1,716	2,801
Deferred revenue	546	953
Stock compensation	13	22
Reserves and other	(115)	404
Total deferred tax assets	30,366	47,037
Valuation allowance	(30,366)	(47,037)
Net deferred tax assets