Note 3 - Investments (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Current	$ 343,000	$ 607,000
Proceeds from Sale and Maturity of Marketable Securities	0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(254,000)	(56,000)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ (10,000)	$ (34,000)