Consolidated Statements of Patronage Capital and Membership Fees - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Components of comprehensive margin:
Net margin	$ 23,596	$ 27,400
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance	962,286	911,087
Components of comprehensive margin:
Net margin	23,596	27,400
Balance	$ 985,882	$ 938,487

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1377-109256

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