Note 7 - Stockholders' Equity (Details Textual) - USD ($)	3 Months Ended			6 Months Ended		41 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2016
Stock Repurchased During Period, Value	$ (0)		$ (0)	$ 127,000	$ 23,000
Common Stock [Member]
Stock Repurchased During Period, Shares (in shares)	(0)		(0)	8,517	1,895
Stock Repurchased During Period, Value	$ (0)		$ (0)	$ (0)	$ (0)
Stock and Warrant Repurchase Plan [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)							35,000,000.0
Warrants Repurchased During Period (in shares)						6,011,926
Warrants Repurchased During Period, Value						$ 14,700,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 12,000,000.0			$ 12,000,000.0
Stock and Warrant Repurchase Plan [Member] | Common Stock [Member]
Stock Repurchased During Period, Shares (in shares)		8,517				875,218
Stock Repurchased During Period, Value		$ 127,000				$ 8,300,000