Additional Information Pertaining to Stock Options (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of stock options vested	$ 40	$ 20	$ 917	$ 927
Total intrinsic value of stock options exercised	$ 2,805	$ 210	$ 5,174	$ 1,121

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration