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Related Party Transactions - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Apr. 30, 2013 | Apr. 30, 2012 | Apr. 30, 2011
Related Party Transaction [Line Items] |  |  |
Total services purchased | $ 6,577 | $ 2,612 | $ 6,067
Outstanding accounts payable | 1,189 | 45 |
Leases monthly payments | 25 |  |
Capital lease expiration date | Apr. 30, 2013 |  |
Extension in lease Period | 5 years |  |
Total expense charged to operations under lease agreement | 286 | 300 | 311
Landfill post-closure cost | 2,491 | 1,560 |
Accrued costs associated with post-closure obligations | 43,170 | 39,629 | 36,407
Recourse loan to an employee outstanding | 147 | 144 |
Landfills [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Landfill owned | 2 |  |
Landfill post-closure cost | 8 | 8 | 8
Accrued costs associated with post-closure obligations | 100 | 84 |
Recourse Debt [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Recourse loan to an employee outstanding | $ 147 | $ 144 |
Interest at Wall Street Journal Prime Rate | 3.25% |  |

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