Note 9 - Fair Value of Financial Instruments (Details Textual) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Warrants and Rights Outstanding	$ 6,132,947	$ 6,116,882
Fair Value, Inputs, Level 1 [Member]
Cash and Cash Equivalents, Fair Value Disclosure	58,700,000	56,700,000
Restricted Cash and Cash Equivalents, Total		5,600,000
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents, Fair Value Disclosure	0
Restricted Cash and Cash Equivalents, Total		$ 90,000,000
The 2016 Warrant [Member]
Warrants and Rights Outstanding	$ 6,100,000