Note 3 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Income Tax Expense (Benefit), Total	$ 0	$ 0
Deferred Tax Assets, Valuation Allowance, Total	67,400		$ 76,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 0
Pre 2019 [Member] | Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total			245,200
Post 2017 [Member] | Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total			$ 64,700