Customer Financing (Detail)	3 Months Ended		6 Months Ended
	Oct. 27, 2018 USD ($)	Oct. 28, 2017 USD ($)	Oct. 27, 2018 USD ($) finance_agreement	Oct. 28, 2017 USD ($)	Apr. 28, 2018 USD ($)	Apr. 29, 2017 USD ($)
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	40,713,000	$ 95,588,000	$ 88,023,000	$ 151,711,000
Revenues from Sale of Financing Contracts	2,734,000	5,967,000	5,225,000	10,227,000
Cash and cash equivalents	165,515,000	$ 101,456,000	165,515,000	$ 101,456,000	$ 62,984,000	$ 94,959,000
Current receivables of finance contracts not yet sold	66,173,000		66,173,000			46,232,000
Unearned income	7,000		7,000			8,000
Finance contracts receivable sold and outstanding	539,426,000		539,426,000
Deferred purchase price	100,182,000		$ 100,182,000			150,404,000
Bad debt write-offs, percentage (less than)			1.00%
Unsettled Financing Arrangements
Customer Financing [Line Items]
Cash and cash equivalents	36,357,000		$ 36,357,000			$ 35,741,000
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	525,000,000		$ 525,000,000
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