Customer Financing (Detail)	3 Months Ended		9 Months Ended
	Jan. 27, 2018 USD ($)	Jan. 28, 2017 USD ($)	Jan. 27, 2018 USD ($) finance_agreement	Jan. 28, 2017 USD ($)	Apr. 29, 2017 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	45,361,000	$ 106,272,000	$ 197,072,000	$ 278,529,000
Revenues from Sale of Financing Contracts	(1,688,000)	2,450,000	8,539,000	16,966,000
Cash and cash equivalents	118,005,000	$ 121,739,000	118,005,000	$ 121,739,000	$ 94,959,000	$ 137,453,000
Current receivables of finance contracts not yet sold	114,521,000		114,521,000		124,098,000
Unearned income	0		0		940,000
Finance contracts receivable sold and outstanding	581,291,000		581,291,000
Deferred purchase price	137,054,000		$ 137,054,000		119,798,000
Bad debt write-offs, percentage (less than)			1.00%
Unsettled Financing Arrangements
Customer Financing [Line Items]
Cash and cash equivalents	36,009,000		$ 36,009,000		$ 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