INVESTMENTS IN OTHER ASSOCIATIONS (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Investment in other associations
Investment in other associations	$ 162,738	$ 161,487
Impairment during the period	0	0
Basin Electric Power Cooperative
Investment in other associations
Investment in other associations	118,115	118,115
National Rural Utilities Cooperative Finance Corporation - patronage capital
Investment in other associations
Investment in other associations	11,761	11,704
National Rural Utilities Cooperative Finance Corporation - capital term certificates
Investment in other associations
Investment in other associations	15,953	16,018
CoBank, ACB
Investment in other associations
Investment in other associations	10,201	9,062
Western Fuels Association
Investment in other associations
Investment in other associations	2,408	2,392
Other
Investment in other associations
Investment in other associations	$ 4,300	$ 4,196

Amount of investment in equity security without readily determinable fair value.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117539-209714

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 321
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-Section 50
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