Note 1 - Basis of Presentation (Details Textual) - USD ($)		1 Months Ended			3 Months Ended		12 Months Ended
	Jan. 01, 2019	Nov. 30, 2018	Mar. 31, 2018	May 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Net Income (Loss) Attributable to Parent, Total					$ (7,260,000)	$ (5,971,000)
Working Capital					13,900,000
Net Cash Provided by (Used in) Operating Activities, Total					(4,035,000)	(3,937,000)
Proceeds from Issuance of Common Stock					$ 7,891,000
Debt Instrument, Convertible, Conversion Price					$ 6.75
Required Payment to Acquire Property Available for Purchase, Due End of Fiscal Year					$ 18,000,000
Percentage of Future Quarterly Interest Payments					25.00%
Interest Payments in Stock					$ 330,000
Debt Conversion, Original Debt, Amount					$ 3,060,000
Stock Issued During Period, Shares, Conversion of Convertible Securities					485,020
Operating Lease, Right-of-Use Asset					$ 103,000
Operating Lease, Liability, Total					90,000
Current Period Reclassification Adjustment	$ 865,000				865,000
Income Taxes Paid							$ 1,000
Additional Paid-in Capital [Member]
Net Income (Loss) Attributable to Parent, Total
Current Period Reclassification Adjustment					2,896,000
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset	151,000
Operating Lease, Liability, Total	100,000
Reclassification of Warrant Liability to Additional Paid-in Capital [Member]
Current Period Reclassification Adjustment					$ 865,000
Gains from Revaluating Warrants							$ 1,500,000	$ 500,000
Reclassification of Warrant Liability to Additional Paid-in Capital [Member] | Additional Paid-in Capital [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	2,000,000
Reclassification of Warrant Liability to Additional Paid-in Capital [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 2,000,000
Senior Secured Debt [Member]
Debt Instrument, Face Amount				$ 60,000,000
Debt Instrument, Additional Amount after Refinance				15,000,000
Convertible Debt, Option Agreements, Percentage					99.00%
Long-term Debt, Total					$ 67,100,000
Debt Instrument, Maturity Date, Percentage of Conversion Rate,					120.00%
Debt Instrument, Maturity Date, Minimum Principal Outstanding Amount					$ 10,000,000
Prior Senior Secured Debt [Member]
Extinguishment of Debt, Amount				$ 45,000,000
2020 Convertible Senior Notes [Member]
Long-term Debt, Maturities, Repayments of Principal and Interest in Year Two					$ 76,300,000
Debt Instrument, Interest Rate, Stated Percentage					7.00%
Debt Instrument, Convertible, Conversion Price					$ 6.75
At Market Issuance Sales Agreement [Member]
At Market Issuance Sales Agreement, Maximum Aggregate Offering Price		$ 25,000,000	$ 15,000,000			$ 15,000,000
Stock Issued During Period, Shares, New Issues		879,920	1,159,718
Proceeds from Issuance of Common Stock, Gross		$ 9,140,000	$ 15,000,000
Proceeds from Issuance of Common Stock		$ 8,810,000	$ 14,600,000