Note 2 - Cash, Cash Equivalents and Marketable Investments - Unrealized Gains and Losses Related to Marketable Investments (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Amortized Cost	$ 11,443,000	$ 13,775,000	$ 6,265,000	$ 10,868,000
Fair Market Value	11,443,000	13,775,000
Amortized Cost	37,003,000	40,311,000
Gross Unrealized Gains	10,000	9,000
Gross Unrealized Losses	(23,000)	(21,000)
Fair Market Value	36,990,000	40,299,000
Amortized Cost	48,446,000	54,086,000
Fair Market Value	48,433,000	54,074,000
US Treasury and Government [Member]
Amortized Cost	4,453,000	8,403,000
Gross Unrealized Gains		4,000
Gross Unrealized Losses	(11,000)	(9,000)
Fair Market Value	4,442,000	8,398,000
US Government Agencies Debt Securities [Member]
Amortized Cost	2,002,000	3,918,000
Gross Unrealized Gains
Gross Unrealized Losses	(2,000)	(2,000)
Fair Market Value	2,000,000	3,916,000
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost		1,325,000
Gross Unrealized Gains
Gross Unrealized Losses
Fair Market Value		1,325,000
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Amortized Cost	17,243,000	12,299,000
Gross Unrealized Gains	3,000	2,000
Gross Unrealized Losses	(1,000)	(2,000)
Fair Market Value	17,245,000	12,299,000
Corporate Debt Securities [Member]
Amortized Cost	13,305,000	14,366,000
Gross Unrealized Gains	7,000	3,000
Gross Unrealized Losses	(9,000)	(8,000)
Fair Market Value	13,303,000	14,361,000
Cash [Member]
Amortized Cost	6,918,000	6,672,000
Fair Market Value	6,918,000	6,672,000
Money Market Funds [Member]
Amortized Cost	1,026,000	6,053,000
Fair Market Value	1,026,000	6,053,000
Commercial Paper [Member]
Amortized Cost	3,499,000	1,050,000
Fair Market Value	$ 3,499,000	$ 1,050,000