Note 7 - Stockholders' Equity (Details Textual) - USD ($)	3 Months Ended		41 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2016
Stock Repurchased During Period, Value	$ 127,000	$ 23,000
Common Stock [Member]
Stock Repurchased During Period, Shares (in shares)	8,517	1,895
Stock Repurchased During Period, Value
Stock and Warrant Repurchase Plan [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)				35,000,000
Warrants Repurchased During Period (in shares)			6,011,926
Warrants Repurchased During Period, Value			$ 14,700,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 12,000,000		$ 12,000,000
Stock and Warrant Repurchase Plan [Member] | Common Stock [Member]
Warrants Repurchased During Period (in shares)	8,517
Warrants Repurchased During Period, Value	$ 127,000
Stock Repurchased During Period, Shares (in shares)			875,218
Stock Repurchased During Period, Value			$ 8,300,000