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Contingencies (Narrative) (Detail) (USD $) In Thousands, unless otherwise specified | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |  |  | 1 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 30, 2011 | May 31, 2009 | Jan. 31, 2013 | Jan. 31, 2012 | Apr. 30, 2011 | Apr. 30, 2010 | Apr. 30, 2009 | Jan. 31, 2009 | Jan. 31, 2013 | Jan. 31, 2012 | Nov. 13, 2012 D | Apr. 30, 2012 | May 31, 2011 | Jan. 18, 2011 | Jan. 30, 2009 | Dec. 20, 2000 acre | Sep. 30, 2011 Waste Stream Inc [Member] | Nov. 30, 2011 Motors Liquidation Trust [Member]
Contingencies And Commitments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disputed invoice amount |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,195 |  |  |  |  |
Aggregate finance asserting liability total |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,852 |  |  |  |
Taxation payable |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,220 |  |  |  |
Penalties and interest payable |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,632 |  |  |  |
Scrap yard and solid waste transfer station |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25 |  |
Undiscounted costs associated with implementing preferred remedies |  | 10,219 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Present worth cost associated with implementing preferred remedies | 12,130 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Enter into a Consent Order with DEC |  |  |  |  |  |  |  |  |  |  | 60 |  |  |  |  |  |  |
Environmental remediation charge |  |  |  |  | 549 | 335 | 1,532 | 2,823 |  |  |  |  |  |  |  |  |  |
Percentage of environmental remediation cost |  |  |  |  |  |  | 15.00% |  |  |  |  |  |  |  | 30.00% |  |  |
Environmental remediation liability |  |  | 5,313 |  |  |  |  |  | 5,313 |  |  | 5,210 |  |  |  |  |  |
Accretion expense |  |  | 34 | 34 |  |  |  |  | 103 | 103 |  |  |  |  |  |  |  |
Percentage of risk free interest rate |  |  | 2.70% |  |  |  |  |  | 2.70% |  |  | 2.70% |  |  |  |  |  |
Future remediation costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,000 | $ 100

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