Note 3 - Income Taxes (Details Textual) - USD ($)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					35.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 716,000	$ 716,000
Unrecognized Tax Benefits, Ending Balance	2,660,000	2,660,000			$ 5,506,000	$ 5,200,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense	(500,000)		$ (400,000)
Minimum [Member]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0	0
Maximum [Member]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ (2,400)	$ (2,400)
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				21.00%