Customer Financing (Detail)	3 Months Ended		6 Months Ended
	Oct. 28, 2017 USD ($)	Oct. 29, 2016 USD ($)	Oct. 28, 2017 USD ($) finance_agreement	Oct. 29, 2016 USD ($)	Apr. 29, 2017 USD ($)	Jul. 30, 2016 USD ($)	Apr. 30, 2016 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	95,588,000	$ 62,663,000	$ 151,711,000	$ 172,257,000
Revenues from Sale of Financing Contracts	5,967,000	$ 4,331,000	10,227,000	$ 14,516,000
Cash and cash equivalents	101,456,000		101,456,000		$ 94,959,000	$ 110,387,000	$ 137,453,000
Current receivables of finance contracts not yet sold	70,193,000		70,193,000		124,098,000
Unearned income	0		0		940,000
Finance contracts receivable sold and outstanding	612,216,000		612,216,000
Deferred purchase price	129,098,000		$ 129,098,000		119,798,000
Bad debt write-offs, percentage (less than)			1.00%
Unsettled Financing Arrangements
Customer Financing [Line Items]
Cash and cash equivalents	32,187,000		$ 32,187,000		$ 17,902,000
The Bank of Tokyo-Mitsubishi UFJ, Ltd.
Customer Financing [Line Items]
Percentage of principal amount of financing contracts held as collateral (at least)			9.50%
Capacity under agreement	575,000,000		$ 575,000,000
Fifth Third Bank
Customer Financing [Line Items]
Percentage of principal amount of financing contracts held as collateral (at least)			11.00%
Capacity under agreement	$ 100,000,000		$ 100,000,000