Loans and Commitments (Details 12) - USD ($) $ in Thousands	Feb. 29, 2016	May. 31, 2015
Pledging of Loans and Loans on Deposit
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 13,081	$ 4,221
Cash	$ 4,268	$ 485
Loans and Leases Receivable Commercial, Net of Deferred Income, Percentage	100.00%	100.00%
Collateral trust bonds 2007 indenture
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	$ 7,488,258	$ 6,708,501
Debt outstanding	6,747,711	6,197,711
Collateral trust bonds 1994 indenture
Pledging of Loans and Loans on Deposit
Debt outstanding	800,000	855,000
Notes payable \| Federal Agricultural Mortgage Corporation
Pledging of Loans and Loans on Deposit
Debt outstanding	2,312,616	1,910,688
Notes payable \| Federal Financing Bank
Pledging of Loans and Loans on Deposit
Debt outstanding	4,786,627	4,406,785
Clean Renewable Energy Bonds Series 2009A
Pledging of Loans and Loans on Deposit
Debt outstanding	14,871	16,529
Cash	0	485
Total pledged collateral	17,656	19,745
Mortgage notes \| Distribution system mortgage notes \| Collateral trust bonds 2007 indenture
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	7,335,292	6,551,836
Mortgage notes \| Distribution system mortgage notes \| Collateral trust bonds 1994 indenture
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	852,944	905,656
Mortgage notes \| Distribution and power supply system mortgage notes \| Federal Agricultural Mortgage Corporation
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	2,736,592	2,160,805
Mortgage notes \| Distribution and power supply system mortgage notes \| Clean Renewable Energy Bonds Series 2009A
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	17,656	19,260
RUS guaranteed loans qualifying as permitted investments \| Collateral trust bonds 2007 indenture
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	152,966	156,665
Mortgage notes receivable on deposit \| Distribution and power supply system mortgage notes \| Federal Financing Bank
Pledging of Loans and Loans on Deposit
Loans outstanding and pledged as collateral	5,404,553	4,943,746
Nonperforming Financing Receivable [Member]
Pledging of Loans and Loans on Deposit
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 2,358	$ 0

Carrying amount as of the balance sheet date of assets that have been pledged as collateral.

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- Definition

Represents the percentage of total loan that is represented by a particular financial receivable category.

+ References

No definition available.

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- References

No definition available.

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- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
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- Definition

Reflects the aggregate value of loans, trade receivables, securities and financial instruments that serve as collateral for obligations arising from a transfer of financial assets recorded as a secured borrowing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
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- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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