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Divestiture Transactions and Discontinued Operations - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 1 Months Ended | 3 Months Ended | 12 Months Ended |  | 3 Months Ended | 12 Months Ended | 3 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 01, 2011 | Apr. 30, 2013 | Jan. 31, 2013 | Jul. 31, 2012 | Oct. 31, 2011 | Jul. 31, 2011 | Apr. 30, 2011 | Apr. 30, 2012 | Apr. 30, 2011 | Jan. 31, 2011 Facility | Jan. 31, 2011 Trilogy Glass [Member] | Apr. 30, 2011 Trilogy Glass [Member] | Jul. 31, 2011 Southeastern Massachusetts [Member]
Divestitures [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on disposal of discontinued operations |  | $ 3,261 |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from purchase and sale agreement | 134,195 |  |  | 6,650 |  |  |  |  |  | 130,400 |  |  | 7,750
Number of material recovery facilities divested |  |  |  |  |  |  |  |  |  | 17 |  |  |
Number of MRFs retained |  |  |  |  |  |  |  |  |  | 4 |  |  |
Commodities marketing agreement period |  |  |  |  |  |  |  |  |  | 10 years |  |  |
Percentage of Purchaser to market commodities |  |  |  |  |  |  |  |  |  | 100.00% |  |  |
Remaining integrated MRFs |  |  |  |  |  |  |  |  |  | 3 |  |  |
Working capital and other purchase price adjustment | 3,795 |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of assets | 122,953 |  |  |  |  |  |  |  |  |  | 1,840 |  | 7,533
Gain (loss) on disposal of discontinued operations, net of tax |  |  |  |  | 79 | 646 | 43,718 | 725 | 43,590 |  |  | 128 |
Undiscounted purchase consideration paid in installments |  |  |  | 21 years |  |  |  |  |  |  |  |  |
Loss on divestiture |  |  | (353) |  |  |  |  |  |  |  |  |  |
Reversal of initial loss on divestiture |  | 353 |  |  |  |  |  |  |  |  |  |  |
Gain on sale of assets |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,502

X
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- Definition Adjustment to the loss on divestiture due to changes in the estimated costs of demolition and site remediation for the divested business. + References No definition available. + Details
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- Definition The percentage of tonnage marketed for three of our retained MRFs by the purchaser of the divested entity. + References No definition available. + Details
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- Definition Adjustment, net of tax, to an amount previously reported in discontinued operations that is directly related to the disposal of the component in a prior period. Examples of circumstances leading to such adjustments include the resolution of contingencies relating to the terms of the disposal transaction or relating to the operations of the component prior to its disposal, and the settlement of certain employee benefit plan obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 44 -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 205 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1510-107760 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e1012-107759 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e1020-107759 + Details
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- Definition The gain (loss) resulting from the sale of a disposal group that is not a discontinued operation. It is included in income from continuing operations before income taxes in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 37, 45 -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 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 47 -Subparagraph b -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2443-110228 + Details
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