Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Available-for-sale Securities, Current	$ 252,000		$ 252,000		$ 607,000	[1]
Proceeds from Sale and Maturity of Marketable Securities			0		$ 0
Marketable Securities, Unrealized Gain (Loss)	(208,000)	$ 28,000	(243,000)	$ (50,000)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 105,000	$ 15,000	$ 113,000	$ 31,000

[1] The condensed consolidated balance sheet as of December 31, 2016 has been prepared using information from the audited consolidated balance sheet as of that date.