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Goodwill and Intangible Assets - Schedule of Activity and Balances Related to Goodwill (Detail) (USD $) In Thousands, unless otherwise specified | 6 Months Ended |  |  |  | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 31, 2014 | Oct. 31, 2013 | Oct. 31, 2014 Eastern Region [Member] | Apr. 30, 2014 Eastern Region [Member] | Oct. 31, 2014 Western Region [Member] | Oct. 31, 2014 Recycling [Member] | Apr. 30, 2014 Recycling [Member] | Oct. 31, 2014 Other [Member] | Apr. 30, 2014 Other [Member]
Goodwill And Intangible Assets [Line Items] |  |  |  |  |  |  |  |  |
Goodwill, beginning balance | $ 119,139 | $ 2,272 | $ 17,429 | $ 17,429 | $ 87,666 | $ 12,315 | $ 12,315 | $ 1,729 | $ 1,729
Acquisitions | 31 |  |  |  | 31 |  |  |  |
Goodwill, ending balance | $ 119,170 | $ 2,272 | $ 17,429 | $ 17,429 | $ 87,697 | $ 12,315 | $ 12,315 | $ 1,729 | $ 1,729

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 + Details
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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