Note 8 - Common Stock (Details Textual)			1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 02, 2017 USD ($) shares	Jan. 31, 2013 shares	May 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Common Stock, Capital Shares Reserved for Future Issuance		400,000
Percentage Of Projects Annual Capacity		51.00%
Number of Milestones for Common Stock Issuance		4
Shares Payable Term From Date Earned		3 years
Allocated Share-based Compensation Expense | $			$ 520,000	$ 171,000	$ 2,303,000	$ 1,296,000	$ 1,116,000
Stock Issued During Period, Value, New Issues | $					3,734,000
Interest Expense [Member] | Issuance of Shares and Cancellation of Warrants [Member]
Allocated Share-based Compensation Expense | $					3,100,000
Prior Lenders [Member]
Stock Issued During Period, Shares, New Issues	264,096
Stock Issued During Period, Value, New Issues | $	$ 3,300,000
Class of Warrant or Right, Number of Securities Called, Cancelled During Period	357,500
Water Project with Brownstein [Member]
Related Party Transaction, Expenses from Transactions with Related Party | $					$ 1,800,000	$ 1,100,000
Shares Earned Upon Execution Of The Revised Agreement [Member]
Common Stock, Capital Shares Reserved for Future Issuance		100,000
Shares Earned Upon Receipt By The Company [Member]
Common Stock, Capital Shares Reserved for Future Issuance		100,000
Shares Earned Upon The Signing Of Binding Agreements [Member]
Common Stock, Capital Shares Reserved for Future Issuance		100,000
Shares Earned Upon The Commencement Of Construction [Member]
Common Stock, Capital Shares Reserved for Future Issuance		100,000