Customer Financing - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Jan. 30, 2016 USD ($)	Jan. 24, 2015 USD ($)	Jan. 30, 2016 USD ($) finance_agreement	Jan. 24, 2015 USD ($)	Apr. 25, 2015 USD ($)	Apr. 26, 2014 USD ($)
Customer Financing [Line Items]
Maximum credit financed for equipment purchases for any one customer	$ 500,000		$ 500,000
Number of customer financing contracts | finance_agreement			2
Financing contracts sold under ASC 860	128,442,000	$ 82,977,000	$ 271,381,000	$ 215,125,000
Cash and cash equivalents	97,701,000	$ 289,722,000	97,701,000	$ 289,722,000	$ 347,260,000	$ 264,908,000
Current receivables of finance contracts not yet sold	92,366,000		92,366,000		88,470,000
Unearned income	3,982,000		3,982,000		4,197,000
Finance contracts receivable sold and outstanding	589,615,000		589,615,000
Deferred purchase price	135,985,000		$ 135,985,000		66,715,000
Bad debt write-offs, percentage, maximum (less than)			1.00%
Unsettled Financing Arrangements [Member]
Customer Financing [Line Items]
Cash and cash equivalents	26,428,000		$ 26,428,000		$ 29,863,000
Fifth Third Bank [Member]
Customer Financing [Line Items]
Capacity under agreement	100,000,000		100,000,000
The Bank of Tokyo-Mitsubishi UFJ, Ltd. [Member]
Customer Financing [Line Items]
Capacity under agreement	$ 575,000,000		$ 575,000,000
Minimum [Member] | Fifth Third Bank [Member]
Customer Financing [Line Items]
Percentage of principal amount of financing contracts held as collateral			15.00%
Minimum [Member] | The Bank of Tokyo-Mitsubishi UFJ, Ltd. [Member]
Customer Financing [Line Items]
Percentage of principal amount of financing contracts held as collateral			25.00%