Schedule of Estimated Annual Amortization Expense (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013
Expected Amortization Expense [Line Items]
Estimated annual amortization expense, For the fiscal year ending July 31, 2013	$ 11,037
Estimated annual amortization expense, For the fiscal year ending July 31, 2014	10,488
Estimated annual amortization expense, For the fiscal year ending July 31, 2015	10,139
Estimated annual amortization expense, For the fiscal year ending July 31, 2016	9,097
Estimated annual amortization expense, For the fiscal year ending July 31, 2017	8,710
Estimated annual amortization expense, For the fiscal year ending July 31, 2018 and thereafter	$ 63,062