Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Schedule Of Income Taxes [Line Items]
Company's effective tax rate	17.50%	(2.80%)	4.10%	(2.70%)
Tax benefit resulting from a reduction in the valuation allowance	$ 2.5