Note 3 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Tax Expense (Benefit), Total	$ 0	$ 0	$ 0	$ 0
Deferred Tax Assets, Valuation Allowance, Total					$ 67,300
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 0		$ 0
Open Tax Year			2013 2014 2015 2016 2017 2018
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent					21.00%
Pre 2018 [Member] | Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total					$ 245,200
Tax Year 2018 [Member] | Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total					$ 25,200
Earliest Tax Year [Member]
Operating Loss Carryforwards, Expiration Date					Jan. 01, 2023