Loans Troubled Debt Restructured Loans (Details) - USD ($) $ in Thousands	May 31, 2020	May 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and Leases Receivable Commercial, Net of Deferred Income, Percentage	100.00%	100.00%
Performing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 10,847	$ 11,853
Performing TDR Loans As Percentage of Total Loans	0.04%	0.05%
TDR Financing Receivable
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 10,847	$ 11,853
Loans and Leases Receivable Commercial, Net of Deferred Income, Percentage	0.04%	0.05%
CFC | Performing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 5,755	$ 6,261
Performing TDR Loans As Percentage of Total Loans	0.02%	0.03%
RTFC | Performing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 5,092	$ 5,592
Performing TDR Loans As Percentage of Total Loans	0.02%	0.02%