Long-Term Debt - Additional Information (Detail) - USD ($)			12 Months Ended
	Jun. 15, 2016	Nov. 23, 2015	Apr. 30, 2016	Apr. 30, 2015
Debt Instrument [Line Items]
Value of common shares repurchases permitted, dividends paid and permitted acquisitions for any fiscal year			$ 135,000,000
Value of common shares repurchases permitted and dividends paid for any fiscal year			85,000,000
Financial covenants amount			50,000,000
Payment of principal			$ 10,000,000
Subsequent Event
Debt Instrument [Line Items]
Long-term debt	$ 275,000,000
Subsequent Event | New Senior Secured Credit Agreement
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	400,000,000
Payment of principal	140,000,000
Line of credit facility borrowings	$ 275,000,000
Minimum
Debt Instrument [Line Items]
Quarterly fee on average daily unused amount of Credit Facilities			0.25%
Maximum
Debt Instrument [Line Items]
Quarterly fee on average daily unused amount of Credit Facilities			0.40%
London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Applicable margin on variable interest rate			1.125%
London Interbank Offered Rate (LIBOR) | Minimum | Subsequent Event | New Senior Secured Credit Agreement
Debt Instrument [Line Items]
Applicable margin on variable interest rate	1.25%
London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Applicable margin on variable interest rate			1.875%
London Interbank Offered Rate (LIBOR) | Maximum | Subsequent Event | New Senior Secured Credit Agreement
Debt Instrument [Line Items]
Applicable margin on variable interest rate	2.00%
Base Rate Loans | Minimum
Debt Instrument [Line Items]
Applicable margin on variable interest rate			0.125%
Base Rate Loans | Minimum | Subsequent Event | New Senior Secured Credit Agreement
Debt Instrument [Line Items]
Applicable margin on variable interest rate	0.25%
Base Rate Loans | Maximum
Debt Instrument [Line Items]
Applicable margin on variable interest rate			0.875%
Base Rate Loans | Maximum | Subsequent Event | New Senior Secured Credit Agreement
Debt Instrument [Line Items]
Applicable margin on variable interest rate	1.00%
Term Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 150,000,000
Line of credit facility, extended maturity date		Sep. 23, 2020	Sep. 23, 2020
Senior unsecured loan, aggregate principal amount		$ 150,000,000
Payment of principal			$ 10,000,000
Long-term debt			$ 140,000,000
Average interest rate			1.65%
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 100,000,000
Line of credit facility, extended maturity date			Sep. 23, 2020
Line of credit facility borrowings			$ 0	$ 0
Letter of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			25,000,000
Standby Letters of Credit
Debt Instrument [Line Items]
Long-term debt arrangement			2,800,000	2,800,000
CSV of COLI Contracts
Debt Instrument [Line Items]
Outstanding policy loans			$ 68,400,000	69,600,000
CSV of COLI Contracts | Minimum
Debt Instrument [Line Items]
Average interest rate			4.76%
CSV of COLI Contracts | Maximum
Debt Instrument [Line Items]
Average interest rate			8.00%
Other Financial Institutions | Standby Letters of Credit
Debt Instrument [Line Items]
Long-term debt arrangement			$ 6,400,000	$ 1,600,000