Retirement Benefits - Summary of Fair Value Assets in Defined Benefit Pension Plans (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 16,288	$ 15,415	$ 14,007
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,025	4,475
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	252	3,186
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16,288	15,415
Level 1 [Member] | Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,034	5,875
Level 1 [Member] | Small/Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,030	1,535
Level 1 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	947
Level 1 [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,025	4,475
Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	252	3,186
Level 1 [Member] | Emerging Market [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		216
Level 1 [Member] | Real Estate And Commodities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		128
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | Small/Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | Emerging Market [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 2 [Member] | Real Estate And Commodities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | Small/Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | Emerging Market [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Level 3 [Member] | Real Estate And Commodities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets