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Business Combinations - Additional Information (Detail)	6 Months Ended
	Oct. 31, 2014 Business	Oct. 31, 2013 Business
Solid Waste Operations [Member]
Business Acquisition [Line Items]
Number of businesses acquired		3
Solid Waste Operations [Member] | Western Region [Member]
Business Acquisition [Line Items]
Number of businesses acquired	1	2
Solid Waste Operations [Member] | Eastern Region [Member]
Business Acquisition [Line Items]
Number of businesses acquired	1	1
Industrial Services [Member] | Other [Member]
Business Acquisition [Line Items]
Number of businesses acquired		1
Minimum [Member]
Business Acquisition [Line Items]
Acquired intangible assets, amortization period	5 years
Maximum [Member]
Business Acquisition [Line Items]
Acquired intangible assets, amortization period	10 years

X

- Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of businesses acquired by the entity during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration