Warranty Reserve - Additional Information (Detail) (USD $)	3 Months Ended
Jul. 31, 2013	Jul. 31, 2012	Apr. 30, 2013	Apr. 30, 2012	Aug. 22, 2013 Subsequent Event M&P Shield TM
Standard Product Warranty Accrual [Line Items]
Accrued warranty	$ 8,327,000	$ 6,278,000	$ 8,423,000	$ 6,412,000	$ 370,000
Remaining cost related to recall costs	3,600,000
Warranty expense	$ 842,000	$ 828,000

Carrying value as of the balance sheet date of obligations incurred through that date and payable for estimated claims under standard and extended warranty protection rights granted to customers.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.15(5))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 15

-Subparagraph 5

-Article 9

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph ((c)(5))

-URI http://asc.fasb.org/extlink&oid=6398077&loc=d3e12565-110249

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