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Note 6 - Financial Instruments and Fair Value (Details Textual) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2016
Jun. 30, 2015
Mar. 31, 2015
Jun. 30, 2014
Dec. 31, 2014
Dec. 31, 2011
Dec. 31, 2015
Auction Rate Securities [Member]              
Available-for-sale Securities $ 6,650,000           $ 6,650,000
Available-for-sale Securities, Amortized Cost Basis $ 7,150,000           $ 7,150,000
Auction Rate Securities Redeemed   $ 275,000   $ 150,000      
Derivative, Basis Spread on Variable Rate 2.25%            
Asset Impairment Charges $ 7,718,000       $ 1,000,000  
Available-for-sale Debt Securities Gross Unrealized Gain         $ 427,000