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Goodwill and Intangible Assets - Schedule of Activity and Balances Related to Goodwill (Parenthetical) (Detail) (Eastern Region [Member], Bestway Disposal Services and BBI Waste Services [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
	Jan. 31, 2014
Eastern Region [Member] | Bestway Disposal Services and BBI Waste Services [Member]
Goodwill And Intangible Assets [Line Items]
Adjustment related to the December 5, 2012	$ 33
Business acquisition date	Dec. 05, 2012

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- Definition

Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 25

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- Definition

This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to intangibles acquired in connection with a business combination for which the initial accounting was incomplete.

+ References

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

-Publisher FASB

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