Note 4 - Investments - Available-for-sale Marketable Securities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	[1]
Unrealized gain recognized in earings since January 1, 2018	$ 32,000
Available-for-sale Securities, Current, Total	375,000		$ 343,000
Marketable Securities [Member]
Cost basis	543,000	543,000
Gains previously recognized on warrants	380,000	380,000
Loss included in accumulated other comprehensive loss or reclassifed to retained earnings on Jaunuary 1, 2018	(580,000)	(580,000)
Unrealized gain recognized in earings since January 1, 2018	32,000
Available-for-sale Securities, Current, Total	$ 375,000	$ 343,000

[1] The condensed consolidated balance sheet as of December 31, 2017 has been prepared using information from the audited consolidated balance sheet as of that date.