Note 2 - Liquidity Risks and Management's Plans (Details Textual) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) shares	Oct. 24, 2016 USD ($) $ / shares	May 24, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Deerfield Loan [Member]
Debt Instrument Repayment of Principal Portion Number of Installments	2
Long-term Debt, Excluding Current Maturities	$ 25,000				$ 25,000
Battelle 2014 Collaboration Agreement [Member]
Accounts Payable and Accrued Liabilities, Current	4,000
Interest and Dividends Payable, Current	$ 300
Common Stock [Member] | Subsequent Event [Member]
Share Price | $ / shares		$ 3.24
Entity Public Float		$ 27,200
Prefunded Warrants [Member] | July 2015 Public Offering [Member]
Class of Warrant or Right, Outstanding | shares	2,900,000
Cash and Cash Equivalents, at Carrying Value	$ 12,383				38,722	$ 46,308	$ 44,711
Accounts Payable and Accrued Liabilities, Current	14,100
Long-term Debt, Excluding Current Maturities	25,000				$ 25,000
Prospectus Supplement to Universal Shelf, Equity Amount			$ 10,500
Prospectus Supplement, Amount that Could Be Raised	$ 9,100		$ 10,500
Excess Percentage of Common Stock Issued to Acquire Additional Capital	20.00%
Common Stock, Shares Authorized | shares	60,000,000				36,000,000
Preferred Stock, Shares Authorized | shares	5,000,000				5,000,000
Common Stock Capital Shares Available for Issuance | shares	40,800,000
Preferred Stock Capital Shares Available for Issuance | shares	5,000,000
Stockholders' Equity Attributable to Parent	$ (22,850)			$ (5,000)	$ 8,266