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Note 8 - Secured Promissory Note Payable to Oxford Finance (Details Textual) - USD ($)		3 Months Ended		6 Months Ended
	Dec. 22, 2016	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Apr. 11, 2019	Feb. 13, 2018
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						10,454,546
Debt Conversion, Converted Instrument, Amount					$ 35,577,000
Warrants in Connection with Loan Agreement [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	7,563						10,914
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 33.11						$ 22.99
Warrants Not Settleable in Cash, Fair Value Disclosure	$ 134,000						$ 70,000
Loan Agreement [Member] \| Oxford Finance [Member]
Long-term Debt, Gross	$ 5,000,000
Debt Instrument, Term	4 years
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	$ 325,000
Debt Instrument, Interest Rate, Stated Percentage	10.50%
Interest Expense, Debt, Total		$ 96,000	$ 138,000	202,000	279,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total		$ 64,000	$ 94,000	$ 136,000	$ 189,000
Debt Conversion, Converted Instrument, Amount	$ 250,000
Loan Agreement [Member] \| Oxford Finance [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	6.17%