Retirement Benefits - Summary of Plan Assets by Asset Categories (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Plan asset	$ 16,288	$ 15,415	$ 14,007
Defined benefit plan, Plan asset percentage	100.00%	100.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Plan asset	11,011	7,754
Defined benefit plan, Plan asset percentage	68.00%	50.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Plan asset	5,025	4,475
Defined benefit plan, Plan asset percentage	31.00%	29.00%
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, Plan asset	$ 252	$ 3,186
Defined benefit plan, Plan asset percentage	1.00%	21.00%