Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	[1]
Available-for-sale Securities, Current, Total	$ 417,000		$ 258,000
Proceeds from Sale and Maturity of Marketable Securities, Total		$ 0
Debt Securities, Available-for-sale, Gain (Loss), Total	170,000	32,000
Debt Securities, Available-for-sale, Unrealized Gain	167,000
Debt Securities, Available-for-sale, Realized Gain	$ 3,000
Debt Securities, Available-for-sale, Unrealized Loss		$ 32,000

[1] The condensed consolidated balance sheet as of December 31, 2018 has been prepared using information from the audited consolidated balance sheet as of that date.