Note 8 - Income Taxes (Details Textual) - USD ($) xbrli-pure in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Deferred Tax Assets, Valuation Allowance, Total	$ 169.1	$ 168.8
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	0.00%
Operating Loss Carryforwards, Total	$ 730.6
Operating Loss Carryforwards, Mortgage Securities	250.3
Operating Loss Carryforwards with No Expiration	$ 95.5
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2025
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Latest Tax Year [Member]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2037