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Note 8 - Secured Promissory Note Payable to Oxford Finance (Details Textual) - USD ($)		3 Months Ended		9 Months Ended
	Dec. 22, 2016	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Feb. 13, 2018
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		$ 82,000	$ 128,000	284,000	407,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total		$ 55,000	$ 87,000	$ 191,000	$ 276,000
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%