Subordinated Deferrable Debt (Details Textual) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Feb. 28, 2014	May 31, 2013
4.75 percent due 2043
Subordinated Deferrable Debt
Amounts Outstanding	$ 400,000	$ 400,000
Interest rate (as a percent)	4.75%	4.75%
Subordinated Deferrable Debt
Subordinated Deferrable Debt
Amounts Outstanding	$ 400,000	$ 400,000

Carrying value as of the balance sheet date of collateralized/uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Subordinated debt places a lender in a lien position behind the primary lender of the company.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_SubordinatedLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant