Intangible Assets - Components of Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2014	Apr. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 33,054	$ 33,005
Less accumulated amortization	(20,321)	(19,585)
Intangible assets, net	12,733	13,420
Covenants Not-to-Compete [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets	17,248	17,245
Less accumulated amortization	(15,500)	(15,363)
Intangible assets, net	1,748	1,882
Client Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets	15,806	15,760
Less accumulated amortization	(4,821)	(4,222)
Intangible assets, net	$ 10,985	$ 11,538