Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Proceeds from Sale and Maturity of Marketable Securities			$ 0		$ 0
Available-for-sale Securities, Current	$ 574,000		574,000		$ 656,000	[1]
Marketable Securities, Unrealized Gain (Loss)	18,000	$ (541,000)	(78,000)	$ (869,000)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 5,000	$ (285,000)	$ (46,000)	$ (490,000)

[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.