Savings Plan, Employee Stock Ownership Plan and Retirement Plan - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
May 31, 2013	May 31, 2012	May 31, 2011
Postemployment Benefits Disclosure [Line Items]
Contributions to Retirement Plan	$ 749	$ 728	$ 483
Other assets	21,346	23,272
Supplemental Executive Retirement Plan [SERP]
Postemployment Benefits Disclosure [Line Items]
Contributions to Retirement Plan	29	30	14
Accrued expense	2,947	2,370
Other assets	$ 2,947	$ 2,370
ESOP
Postemployment Benefits Disclosure [Line Items]
ESOP termination date	2013

The amount of the cost recognized during the period for defined contribution plans.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration