Long-Term Debt and Capital Leases - Components of Long Term Debt and Capital Leases (Detail) (USD $)	Apr. 30, 2013	Apr. 30, 2012
Debt Instrument [Line Items]
Long Term Debt And Capital Lease Obligations Current And Non Current	$ 494,388,000	$ 474,609,000
Less-current maturities	857,000	1,228,000
Non Current Portion Of Long Term Debt And Capital Lease Obligation	493,531,000	473,381,000
Senior subordinated notes due 2019 notes [Member]
Debt Instrument [Line Items]
Senior subordinated notes due	323,265,000	200,000,000
Senior secured revolving credit facility, due 2016 [Member]
Debt Instrument [Line Items]
Senior secured revolving credit facility	123,200,000	69,600,000
Senior second lien notes, due 2014 [Member]
Debt Instrument [Line Items]
Senior second lien notes due		177,428,000
Revenue Bonds Series 2005R-2, due 2025 [Member]
Debt Instrument [Line Items]
FAME Bonds fixed	21,400,000	21,400,000
Long-Term Revenue Bonds Series 2013 due April 1, 2036 [Member]
Debt Instrument [Line Items]
Long-term Revenue Fixed	16,000
Revenue Bonds Series 2013 due April 1, 2029 [Member]
Debt Instrument [Line Items]
Revenue Bond Variable	5,500	0
Revenue Bonds Series, 2005R-1, due 2025 [Member]
Debt Instrument [Line Items]
FAME Bonds variable	3,600,000	3,600,000
Notes payable [Member]
Debt Instrument [Line Items]
Notes payable	1,228,000	2,033,000
Capital lease obligations [Member]
Debt Instrument [Line Items]
Capital leases for facilities and equipment	$ 195,000	$ 548,000

Tax exempt solid waste disposal revenue bonds with a fixed rate.

No definition available.

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Tax exempt solid waste disposal revenue bonds with a variable rate.

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- Definition

Obligation related to long-term debt (excluding convertible debt) and capital leases.

+ References

No definition available.

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Tax exempt solid waste disposal revenue bonds issued by the New Hampshire Business Finance Authority Bonds with a variable rate.

+ References

No definition available.

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Tax exempt solid waste disposal revenue bonds issued by the Vermont Economic Development Authority with a fixed rate.

+ References

No definition available.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount borrowed under the credit facility as of the balance sheet date.

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Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer plus capital lease obligations due to be paid more than one year after the balance sheet date.

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Obligation related to long-term debt (excluding convertible debt) and capital leases, the portion which is due in one year or less in the future.

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Including the current and noncurrent portions, the carrying value of notes payable which were initially due after one year or beyond the normal operating cycle, if longer, and which are not otherwise defined in the taxonomy.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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