Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Feb. 28, 2014		Feb. 28, 2013		Feb. 28, 2014		Feb. 28, 2013
Components of interest income
Interest on investments	$ 1,932		$ 1,864		$ 5,685		$ 4,378
Fee income	3,054	[1]	1,841	[1]	8,224	[1]	5,745	[1]
Total interest income	238,732		234,021		719,057		715,736
Long-term fixed-rate loans
Components of interest income
Total interest income	220,227		216,716		666,762		652,903
Long-term variable-rate loans
Components of interest income
Total interest income	5,217		5,203		14,871		16,121
Line of credit loans
Components of interest income
Total interest income	8,302		7,961		23,379		23,066
Restructured loans
Components of interest income
Total interest income	$ 0		$ 436		$ 136		$ 13,523

[1] Primarily related to conversion fees that are deferred and recognized using the effective interest method over the remaining original loan interest rate pricing term, except for a small portion of the total fee charged to cover administrative costs related to the conversion, which is recognized immediately.