Summary Information Regarding Income Tax Related Interest and Penalties (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2010
Income Tax Contingency [Line Items]
Net reduction in interest and penalties	$ (227)	$ (628)	$ (1,029)

The sum of the amounts of estimated penalties and interest recognized in the period arising from income tax examinations.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

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