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Final Capping, Closure and Post-Closure Costs (Tables) | 12 Months Ended
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Apr. 30, 2014
Asset Retirement Obligation Disclosure [Abstract] |
Changes to Accrued Capping, Closure and Post-Closure Liabilities | The changes to accrued final capping, closure and post-closure liabilities for fiscal years 2014 and 2013 are as follows:
|  | Fiscal Year Ended April 30, |
|  | 2014 |  |  | 2013 |
Beginning balance |  | $ | 43,170 |  |  | $ | 39,629 |
Obligations incurred |  |  | 3,621 |  |  |  | 3,188 |
Revisions in estimates (1) |  |  | (3,728 | ) |  |  | (694 | )
Accretion expense |  |  | 3,967 |  |  |  | 3,538 |
Payments |  |  | (2,376 | ) |  |  | (2,491 | )
Ending balance |  | $ | 44,654 |  |  | $ | 43,170 |
(1) | The revisions in estimates for final capping, closure and post-closure for fiscal years 2014 and 2013 consist of changes in cost estimates and the timing of final capping and closure events, as well as changes to expansion airspace and tonnage placement assumptions.

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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