Summary of Significant Accounting Policies - Interest Income (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income		$ 287,037	$ 281,253	$ 577,052	$ 559,744
Investment Income, Interest		5,589	6,135	11,415	11,918
Long Term Fixed Rate Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	[1]	260,714	253,340	519,192	505,141
Long-term variable-rate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income		8,131	10,066	17,887	19,447
Line of credit loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income		12,678	11,752	28,711	23,385
Restructured loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	[2]	212	211	418	429
Other Income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	[3]	287	251	571	576
Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income		$ 281,448	$ 275,118	$ 565,637	$ 547,826

[1] Includes loan conversion fees, which are generally deferred and recognized as interest income using the effective interest method.

[2] Troubled debt restructured (“TDR”) loans.

[3] Consists of late payment fees, commitment fees and net amortization of deferred loan fees and loan origination costs.