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Goodwill and Intangible Assets - Components of Intangible Assets (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2014
Apr. 30, 2013
Finite-Lived Intangible Assets [Line Items]    
Intangible assets $ 33,005 $ 28,703
Less accumulated amortization (18,833) (17,029)
Intangible assets, net 14,172 11,674
Covenants Not-to-Compete [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Intangible assets 17,245 17,043
Less accumulated amortization (15,224) (14,800)
Intangible assets, net 2,021 2,243
Client Lists [Member]
    
Finite-Lived Intangible Assets [Line Items]    
Intangible assets 15,760 11,660
Less accumulated amortization (3,609) (2,229)
Intangible assets, net $ 12,151 $ 9,431