Customer Financing (Detail)	3 Months Ended		9 Months Ended
	Jan. 26, 2019 USD ($)	Jan. 27, 2018 USD ($)	Jan. 26, 2019 USD ($) finance_agreement	Jan. 27, 2018 USD ($)	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	107,715,000	$ 45,361,000	$ 195,738,000	$ 197,072,000
Revenues from Sale of Financing Contracts	6,641,000	(1,688,000)	11,866,000	8,539,000
Cash and cash equivalents	117,431,000	$ 118,005,000	117,431,000	$ 118,005,000	$ 62,984,000	$ 94,959,000
Current receivables of finance contracts not yet sold	69,772,000		69,772,000		46,232,000
Unearned income	41,000		41,000		8,000
Finance contracts receivable sold and outstanding	571,664,000		571,664,000
Deferred purchase price	111,461,000		$ 111,461,000		150,404,000
Bad debt write-offs, percentage (less than)			1.00%
Unsettled Financing Arrangements
Customer Financing [Line Items]
Cash and cash equivalents	33,850,000		$ 33,850,000		$ 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