Consolidated Statements of Patronage Capital and Membership Fees and Accumulated Other Comprehensive (Deficit) Margin - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Increase (Decrease) in Members' Capital
Balance	$ 859,440	$ 809,523
Components of comprehensive margin:
Net margin	21,454	20,598
Unrealized gain (loss) on available-for-sale securities	(39)	284
Balance	880,855	830,405
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance	859,810	809,465
Components of comprehensive margin:
Net margin	21,454	20,598
Balance	881,264	830,063
Accumulated Other Comprehensive (Deficit) Margin
Increase (Decrease) in Members' Capital
Balance	(370)	58
Components of comprehensive margin:
Unrealized gain (loss) on available-for-sale securities	(39)	284
Balance	$ (409)	$ 342

Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569643-111683

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=64809438&loc=SL4573702-111684

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569616-111683

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration