Summary of Significant Accounting Policies - Interest Income Table (Details) (USD $)	3 Months Ended
	Aug. 31, 2014		Aug. 31, 2013		May 31, 2014
Components of interest income
Interest income	$ 237,291,000		$ 241,071,000
Interest on investments	2,572,000		1,936,000
Fee income	3,001,000	[1]	2,016,000	[2]
Deferred conversion fees	75,000,000				73,000,000
Long-term fixed-rate loans
Components of interest income
Interest income	219,416,000		224,583,000
Long-term variable-rate loans
Components of interest income
Interest income	5,360,000		4,828,000
Line of credit loans
Components of interest income
Interest income	6,942,000		7,572,000
Restructured loans
Components of interest income
Interest income	$ 0		$ 136,000

[1] Represents interest expense and the amortization of discounts on debt.

[2] Primarily related to conversion fees, which are deferred and recognized in interest income over the original loan interest rate pricing term using the effective interest method. Also includes a small portion of conversion fees that are intended to cover the administrative costs related to the conversion, which are recognized immediately.