DERIVATIVES. (Details) - Non Designated Derivative Instruments [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cash Collateral Balance [Member]
Derivative assets	$ 3,813	$ 4,331
Commodity Contracts [Member]
Derivative assets	998	978
Derivative liabilities	$ 2,307	$ 4,115

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant