Customer Financing (Detail)	3 Months Ended		9 Months Ended
	Jan. 28, 2017 USD ($)	Jan. 30, 2016 USD ($)	Jan. 28, 2017 USD ($) finance_agreement	Jan. 30, 2016 USD ($)	Apr. 30, 2016 USD ($)	Apr. 25, 2015 USD ($)
Customer Financing [Line Items]
Maximum credit financed for equipment purchases for any one customer	$ 1,000,000		$ 1,000,000
Number of customer financing contracts | finance_agreement			2
Financing contracts sold under ASC 860	106,272,000	$ 128,442,000	$ 278,529,000	$ 271,381,000
Revenues from Sale of Financing Contracts	2,450,000	8,814,000	16,966,000	23,717,000
Cash and cash equivalents	121,739,000	$ 97,701,000	121,739,000	$ 97,701,000	$ 137,453,000	$ 347,260,000
Current receivables of finance contracts not yet sold	96,284,000		96,284,000		87,406,000
Unearned income	2,914,000		2,914,000		1,768,000
Finance contracts receivable sold and outstanding	619,361,000		619,361,000
Deferred purchase price	128,015,000		$ 128,015,000		108,837,000
Bad debt write-offs, percentage (less than)			1.00%
Unsettled Financing Arrangements [Member]
Customer Financing [Line Items]
Cash and cash equivalents	22,363,000		$ 22,363,000		$ 27,186,000
The Bank of Tokyo-Mitsubishi UFJ, Ltd. [Member]
Customer Financing [Line Items]
Percentage of principal amount of financing contracts held as collateral (at least)			9.00%
Capacity under agreement	575,000,000		$ 575,000,000
Fifth Third Bank [Member]
Customer Financing [Line Items]
Percentage of principal amount of financing contracts held as collateral (at least)			10.00%
Capacity under agreement	$ 100,000,000		$ 100,000,000