Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Proceeds from Sale and Maturity of Marketable Securities			$ 0			$ 0
Available-for-sale Securities, Current	$ 617,000			$ 617,000		$ 656,000	[1]
Marketable Securities, Unrealized Gain (Loss)	28,000	$ (452,000)		(50,000)	$ (1,321,000)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 15,000	$ (238,000)		$ 31,000	$ 728,000

[1] The condensed consolidated balance sheet as of December 31, 2015 has been prepared using information from the audited consolidated balance sheet as of that date.