Note 4 - Income Taxes - Deferred Tax Valuation Allowance (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance at Beginning Period	$ 3,393,000	$ 3,530,000	$ 3,583,000
Changes in estimated realization of deferred tax assets	2,400,000	(100,000)
Balance at end of period	5,826,000	3,393,000	3,530,000
Charge to Costs and Expenses [Member]
Changes in estimated realization of deferred tax assets	5,654,000	1,081,000
Charges to Other Accounts [Member]
Changes in estimated realization of deferred tax assets			(31,000)
Deductions [Member]
Changes in estimated realization of deferred tax assets	$ 3,221,000	$ 1,218,000	$ 22,000