Note 2 - Unrealized Gains and Losses Related to Marketable Investments (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Cash [Member]
Amortized Cost	$ 5,528,000	$ 9,830,000
Cash Equivalents	5,528,000	9,830,000
Money Market Funds [Member]
Amortized Cost	1,343,000	1,000,000
Cash Equivalents	1,343,000	1,000,000
Commercial Paper [Member]
Amortized Cost	549,000	38,000
Cash Equivalents	549,000	38,000
US Treasury and Government [Member]
Amortized Cost	12,218,000	7,780,000
Available-for-sale securities	12,240,000	7,779,000
Gross Unrealized Gains		1,000
Gross Unrealized Losses		(2,000)
US Government Agencies Debt Securities [Member]
Amortized Cost	4,027,000	12,630,000
Available-for-sale securities	4,028,000	12,608,000
Gross Unrealized Gains	1,000	3,000
Gross Unrealized Losses		(25,000)
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	2,752,000	4,344,000
Available-for-sale securities	2,758,000	4,346,000
Gross Unrealized Gains	6,000	2,000
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	5,585,000	4,041,000
Available-for-sale securities	5,587,000	4,040,000
Gross Unrealized Gains	2,000	1,000
Gross Unrealized Losses		(2,000)
Corporate Debt Securities [Member]
Amortized Cost	11,279,000	8,783,000
Available-for-sale securities	11,289,000	8,766,000
Gross Unrealized Gains	12,000
Gross Unrealized Losses	(2,000)	(17,000)
Amortized Cost	7,420,000	10,868,000	$ 11,627,000	$ 9,803,000
Cash Equivalents	7,420,000	10,868,000
Amortized Cost	35,861,000	37,578,000
Available-for-sale securities	35,902,000	37,539,000
Gross Unrealized Gains	43,000	7,000
Gross Unrealized Losses	(2,000)	(46,000)
Amortized Cost	43,281,000	48,446,000
Fair Market Value	$ 43,322,000	$ 48,407,000