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Intangible Assets and Goodwill - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Finite-Lived Intangible Assets [Line Items]
Intangible amortization expenses	$ 1,306	$ 629	$ 840
Eastern region [Member]
Finite-Lived Intangible Assets [Line Items]
Fair value in excess of carrying value of goodwill	22.70%
Western region [Member]
Finite-Lived Intangible Assets [Line Items]
Fair value in excess of carrying value of goodwill	23.30%
Recycling [Member]
Finite-Lived Intangible Assets [Line Items]
Fair value in excess of carrying value of goodwill	20.80%

X

- Definition

The percentage by which fair value of the reporting unit exceeded its carrying value.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph a(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275

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Balance Type:	debit
Period Type:	duration

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- Details

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