Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Available-for-sale Securities, Current, Total	$ 375,000		$ 343,000	[1]
Proceeds from Sale and Maturity of Marketable Securities, Total	0		$ 0
Available-for-sale Securities, Gross Unrealized Gain, Total	32,000
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax		(77,000)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax		$ 30,000

[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.