Note 2 - Cash, Cash Equivalents and Marketable Investments (Details) - Unrealized Gains and Losses Related to Marketable Investments (USD $)	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Cash and cash equivalents:
Cash and cash equivalents Amortized Cost	$ 10,902,000	$ 16,242,000	$ 11,885,000	$ 23,546,000
Cash and cash equivalents Fair Market Value	10,902,000	16,242,000
Marketable investments:
Marketable Investments Amortized Cost	70,568,000	66,730,000
Gross Unrealized Gains	132,000	114,000
Gross Unrealized Losses	(4,000)	(13,000)
Marketable Investments Fair Market Value	70,696,000	66,831,000
Cash and cash equivalents and Marketable Investments Amortized Cost	81,470,000	82,972,000
Gross Unrealized Gains	132,000	114,000
Gross Unrealized Losses	(4,000)	(13,000)
Cash and cash equivalents and Marketable Investments Fair Market Value	81,598,000	83,073,000
US Treasury and Government [Member]
Marketable investments:
Marketable Investments Amortized Cost	17,109,000	10,516,000
Gross Unrealized Gains	28,000	11,000
Gross Unrealized Losses		(5,000)
Marketable Investments Fair Market Value	17,137,000	10,522,000
Gross Unrealized Gains	28,000	11,000
Gross Unrealized Losses		(5,000)
US Government Agencies Debt Securities [Member]
Marketable investments:
Marketable Investments Amortized Cost	21,040,000	25,823,000
Gross Unrealized Gains	39,000	38,000
Gross Unrealized Losses		(3,000)
Marketable Investments Fair Market Value	21,079,000	25,858,000
Gross Unrealized Gains	39,000	38,000
Gross Unrealized Losses		(3,000)
US States and Political Subdivisions Debt Securities [Member]
Marketable investments:
Marketable Investments Amortized Cost	3,830,000	2,043,000
Gross Unrealized Gains	5,000	1,000
Gross Unrealized Losses	(3,000)	(5,000)
Marketable Investments Fair Market Value	3,832,000	2,039,000
Gross Unrealized Gains	5,000	1,000
Gross Unrealized Losses	(3,000)	(5,000)
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
Marketable investments:
Marketable Investments Amortized Cost	9,834,000	10,239,000
Gross Unrealized Gains	4,000	3,000
Marketable Investments Fair Market Value	9,838,000	10,242,000
Gross Unrealized Gains	4,000	3,000
Corporate Debt Securities [Member]
Marketable investments:
Marketable Investments Amortized Cost	18,755,000	18,109,000
Gross Unrealized Gains	56,000	61,000
Gross Unrealized Losses	(1,000)
Marketable Investments Fair Market Value	18,810,000	18,170,000
Gross Unrealized Gains	56,000	61,000
Gross Unrealized Losses	(1,000)
Cash [Member]
Cash and cash equivalents:
Cash and cash equivalents Amortized Cost	5,154,000	3,816,000
Cash and cash equivalents Fair Market Value	5,154,000	3,816,000
Money Market Funds [Member]
Cash and cash equivalents:
Cash and cash equivalents Amortized Cost	2,749,000	9,926,000
Cash and cash equivalents Fair Market Value	2,749,000	9,926,000
Commercial Paper [Member]
Cash and cash equivalents:
Cash and cash equivalents Amortized Cost	2,999,000	2,500,000
Cash and cash equivalents Fair Market Value	$ 2,999,000	$ 2,500,000