DERIVATIVES. (Details) - Non Designated Derivative Instruments [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash Collateral Balance [Member]
Derivative assets	$ 4,409	$ 8,479
Commodity Contracts [Member]
Derivative assets	1,155	1,765
Derivative liabilities	$ 5,156	$ 6,309

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

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