Loans - Troubled Debt Restructured Loans (Details) $ in Thousands	12 Months Ended
	May 31, 2023 USD ($) borrower	Aug. 31, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of Total Loans Outstanding	100.00%	100.00%
Total TDR loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Borrowers | borrower	3
Outstanding Amount | $	$ 31,105
% of Total Loans Outstanding	0.10%
Performing TDR loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Borrowers | borrower	2
Outstanding Amount | $	$ 8,230
% of Total Loans Outstanding	0.03%
Nonperforming TDR loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Borrowers | borrower	1
Outstanding Amount | $	$ 22,875
% of Total Loans Outstanding	0.07%
Parent Company
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of Total Loans Outstanding	96.00%	96.00%
Parent Company | Distribution
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of Total Loans Outstanding	78.00%	78.00%
Parent Company | Power supply
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of Total Loans Outstanding	17.00%	17.00%
Parent Company | Total TDR loans | Distribution
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Borrowers | borrower	1
Outstanding Amount | $	$ 4,638
% of Total Loans Outstanding	0.02%
Parent Company | Total TDR loans | Power supply
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Borrowers | borrower	1
Outstanding Amount | $	$ 22,875
% of Total Loans Outstanding	0.07%
RTFC
Financing Receivable, Troubled Debt Restructuring [Line Items]
% of Total Loans Outstanding	1.00%	2.00%
RTFC | Total TDR loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Borrowers | borrower	1
Outstanding Amount | $	$ 3,592
% of Total Loans Outstanding	0.01%