Note 7 - Fair Value of Financial Instruments (Details Textual) - Henry Hub Natural Gas Future ("NG") Contracts [Member] - Put Option [Member] $ in Millions	Jan. 12, 2017 USD ($) MMBTU $ / BTU
Derivative, Nonmonetary Notional Amount, Energy Measure \| MMBTU	4.1
Derivative, Price Risk Option Strike Price \| $ / BTU	3
Payments for Derivative Instrument, Investing Activities \| $	$ 0.7

The cash outflow for derivative instruments during the period, which are classified as investing activities, excluding those designated as hedging instruments.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

Name:	us-gaap_PaymentsForDerivativeInstrumentInvestingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration