Note 4 - Investments (Details Textual) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Available-for-sale Securities, Current	$ 564,000		$ 564,000		$ 607,000	[1]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	22,000	$ 5,000	8,000	$ 46,000
Proceeds from Sale and Maturity of Marketable Securities			0		$ 0
Marketable Securities, Unrealized Gain (Loss)	$ 43,000	$ 18,000	$ 35,000	$ 78,000

[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.