Note 1 - Basis of Presentation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Mar. 31, 2018	May 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Income (Loss) Attributable to Parent, Total			$ (6,240)	$ (5,992)	$ (18,243)	$ (26,789)
Working Capital			$ 15,200		15,200
Net Cash Provided by (Used in) Operating Activities, Total					(8,644)	(7,726)
Proceeds from Issuance of Common Stock					$ 14,581
Debt Instrument, Convertible, Conversion Price			$ 6.75		$ 6.75
Percentage of Future Quarterly Interest Payments			25.00%		25.00%
Interest Payments in Stock					$ 958
Debt Conversion, Original Debt, Amount					$ 2,110
Stock Issued During Period, Shares, Conversion of Convertible Securities					279,480
124-mile Extension Possible for Northern Pipeline, Available for Purchase [Member]
Required Payment to Acquire Property Available for Purchase, Due End of Fiscal Year			$ 20,000		$ 20,000
Senior Secured Debt [Member]
Debt Instrument, Face Amount		$ 60,000
Debt Instrument, Additional Amount after Refinance		15,000
Long-term Debt, Total			65,100		$ 65,100
Debt Instrument, Maturity Date, Percentage of Conversion Rate,					120.00%
Prior Senior Secured Debt [Member]
Extinguishment of Debt, Amount		$ 45,000
2020 Convertible Senior Notes [Member]
Long-term Debt, Maturities, Repayments of Principal and Interest in Year Two			$ 80,300		$ 80,300
Debt Instrument, Convertible, Conversion Price			$ 6.75		$ 6.75
At Market Issuance Sales Agreement [Member]
At Market Issuance Sales Agreement, Maximum Aggregate Offering Price	$ 15,000
Stock Issued During Period, Shares, New Issues	1,159,718
Proceeds from Issuance of Common Stock, Gross	$ 15,000
Proceeds from Issuance of Common Stock	$ 14,600