Note 6 - Note Payable (Details Textual) - USD ($)		3 Months Ended
	May 22, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Interest Payable		$ 15,135,000
Notes Payable, Noncurrent, Total		$ 30,927,000		$ 30,528,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		642,622
May 2017 Issuance Related to 2017 Loan Agreement [Member]
Warrants and Rights Outstanding, Term	10 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	222,049	222,049
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 9.50	$ 9.50
The 2017 Loan Agreement [Member] | CRG LP [Member]
Debt Instrument, Face Amount	$ 20,000,000
Debt Agreement, Covenant, Additional Funding	10,000,000
Debt Agreement, Maximum Borrowing Capacity	$ 30,000,000
Debt Instrument, Term	6 years
Debt instrument, Interest Only Payment, Period	4 years
Debt Instrument, Interest Rate, Stated Percentage	12.50%
Debt Instrument, Interest Rate, Stated Percentage Deferred During Interest-only Period	4.00%
Paid-in-Kind Interest		$ 318,000	$ 305,000
Debt Instrument, Prepayment Fee, Percentage	5.00%
Debt Instrument, Prepayment Fee, Period of Term	5 years
Debt Instrument, Covenant, Cash and Cash Equivalents	$ 2,000,000
Notes Payable, Noncurrent, Total		30,927,000		$ 30,528,000
The 2017 Loan Agreement [Member] | CRG LP [Member] | Other Noncurrent Liabilities [Member]
Interest Payable		$ 573,000