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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Summary Of Significant Accounting Policies [Line Items]            
Capitalized interest       $ 368 $ 407 $ 1,078
Estimate of inflation rate       2.70% 2.70%  
Maximum rate of asset retirement obligation 10.00%     10.00%    
Minimum rate of asset retirement obligation 8.50%     8.50%    
Accretion expense       (3,538) (3,341)  
Goodwill impairment incurred       0 0 0
Estimated useful life of goodwill       10 years    
Asset impairment charge   40,746 3,654   40,746 3,654
Buyers borrowing rate   3.50%        
Recognize loss associated with fair value discontinued operation 3,261          
Maximum exposure workers' compensation plan per individual event       1,000    
Self insurance reserves 11,362 12,024   11,362 12,024  
Maximum cash equivalents maturity period Three months          
Inventory of finished goods and supplies 3,494 3,503   3,494 3,503  
Impairment of equity method investment         10,680  
Equity method investment 3,766 6,795   3,766 6,795  
Derivative instrument interest rate 6.70%     6.70%    
Total notional amount 150,000     150,000    
LIBOR base rate 1.40%     1.40%    
Derivative Instrument maturity term       Mar. 15, 2016    
Interest rate derivative agreements and discontinued hedge 75,000     75,000    
Loss on derivative instruments       3,626    
Concentration of credit risk       At April 30, 2013 and 2012, no single group or customer represented greater than 5% of total accounts receivable-trade.    
Maximum percentage of accounts receivable represented by single group or customer 5.00%     5.00%    
Second Lien Notes [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Derivative instrument interest rate   11.00%     11.00%  
GreenFiber [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Goodwill impairment incurred         5,090  
Asset impairment charge       531    
Equity method investment membership interest 50.00%     50.00%    
Impairment of equity method investment         10,680  
Equity method investment 3,509 6,502   3,509 6,502  
Loan and security agreement guaranty 2,200     2,200    
Payment to satisfy the guaranty and pay off the term loan in full       2,073    
Additional equity method investment 2,073     2,073    
Tompkins [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Equity method investment membership interest 50.00%     50.00%    
Equity method investment 257 293   257 293  
Automobile Plan [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Maximum exposure workers' compensation plan per individual event       750    
Buildings [Member] | Maximum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       30 years    
Buildings [Member] | Minimum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       25 years    
Machinery and equipment [Member] | Maximum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       10 years    
Machinery and equipment [Member] | Minimum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       5 years    
Maintenance equipment [Member] | Maximum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       10 years    
Maintenance equipment [Member] | Minimum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       5 years    
Rolling stock [Member] | Maximum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       10 years    
Rolling stock [Member] | Minimum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       5 years    
Containers [Member] | Maximum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       12 years    
Size of containers       40    
Containers [Member] | Minimum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       5 years    
Size of containers       2    
Residential Carts And Recycling Bins [Member] | Maximum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       10 years    
Residential Carts And Recycling Bins [Member] | Minimum [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Property, plant and equipment, estimated useful life       5 years    
Landfills [Member]
            
Summary Of Significant Accounting Policies [Line Items]            
Accretion expense       3,538 3,341 3,193
Surety bond       128,551 124,600  
Letters of credit $ 1,752 $ 1,752   $ 1,752 $ 1,752