Customer Financing (Details)	3 Months Ended		6 Months Ended
	Oct. 29, 2016 USD ($)	Oct. 31, 2015 USD ($)	Oct. 29, 2016 USD ($) finance_agreement	Oct. 31, 2015 USD ($)	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	62,663,000	$ 48,172,000	$ 172,257,000	$ 142,939,000
Revenues from Sale of Financing Contracts	4,331,000	9,016,000	14,516,000	14,903,000
Cash and cash equivalents	110,387,000	$ 95,451,000	110,387,000	$ 95,451,000	$ 137,453,000	$ 347,260,000
Current receivables of finance contracts not yet sold	82,591,000		82,591,000		87,406,000
Unearned income	2,334,000		2,334,000		1,768,000
Finance contracts receivable sold and outstanding	600,760,000		600,760,000
Deferred purchase price	118,059,000		$ 118,059,000		108,837,000
Bad debt write-offs, percentage (less than)			1.00%
Unsettled Financing Arrangements [Member]
Customer Financing [Line Items]
Cash and cash equivalents	22,809,000		$ 22,809,000		$ 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