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Asset Impairments and Other Items - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |  | 12 Months Ended | 3 Months Ended | 12 Months Ended
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Apr. 30, 2014 | Apr. 30, 2013 | Apr. 30, 2012 | Apr. 30, 2014 Tompkins [Member] | Apr. 30, 2013 BBI Acquisition [Member] | Apr. 30, 2014 Western Region [Member] Cares [Member] | Apr. 30, 2012 New York [Member] | Apr. 30, 2012 Vermont [Member] | Apr. 30, 2014 Maine Energy Facility [Member] | Apr. 30, 2013 Maine Energy Facility [Member] | Apr. 30, 2012 Maine Energy Facility [Member] | Apr. 30, 2012 Maine Energy Facility [Member] Eastern Region [Member] | Apr. 30, 2014 Legal Costs [Member] Tompkins [Member] | Apr. 30, 2013 Legal Costs [Member] BBI Acquisition [Member] | Apr. 30, 2013 Second Lien Notes [Member] BBI Acquisition [Member]
Asset Retirement Obligation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment charge | $ 7,455 |  | $ 40,746 |  |  | $ 7,455 |  |  |  |  |  | $ 40,746 |  |  |
Discount rate |  |  |  |  |  |  |  |  |  |  |  | 3.50% |  |  |
Development project charge | 1,394 |  | 131 |  |  |  |  |  | 1,394 |  | 131 |  |  |  |
Deferred project costs | 0 | 1,644 |  |  |  |  |  |  |  |  |  |  |  |  |
Severance and reorganization charge | 586 | 3,709 |  |  |  |  |  |  |  |  |  |  |  |  |
Liability associated with severance and reorganization | 478 | 680 |  |  |  |  |  |  |  |  |  |  |  |  |
Legal costs for the acquisition | 144 | 1,410 |  |  | 1,410 |  |  |  |  | 505 |  |  | 144 | 602 | 303
Equity method investment membership interest |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |
Legal settlement expenses |  |  | $ 1,359 |  |  |  | $ 359 | $ 1,000 |  |  |  |  |  |  |

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- Definition Amount recognized as an operating expense or loss during the period to write-off the deferred costs associated with development projects no longer deemed viable. + References No definition available. + Details
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- Definition The write-off of costs associated with a financing initiative that is no longer being pursued, legal costs associated with a divestiture and costs associated with an acquisition. + References No definition available. + Details
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- Definition The remaining liability associated with severance and reorganization. + References No definition available. + Details
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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: 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=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228 + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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- Definition Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
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- Definition Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 + Details
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- Definition Gross amount of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs or deferred acquisition costs of insurance companies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation. + References Reference 1: 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=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.P.3) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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