Note 8 - Income Taxes (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 2,400,000		$ 2,400,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	139,000		139,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0		$ 0
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Amount	$ 76,000	$ 22,000
Domestic Tax Authority [Member]
Open Tax Year	2015 2016 2017 2018
State and Local Jurisdiction [Member]
Open Tax Year	2014 2015 2016 2017 2018