3. Costs and Estimated Earnings in Excess of Billings (Details) (USD $)	12 Months Ended
Apr. 30, 2013	Apr. 30, 2012
3. Costs and Estimated Earnings in Excess of Billings (Details) [Line Items]
Revenues	$ 68,932,000	$ 63,595,000
Contracts Accounted for under Percentage of Completion [Member]
3. Costs and Estimated Earnings in Excess of Billings (Details) [Line Items]
Revenues	$ 35,600,000	$ 36,100,000

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration