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Income Taxes - Summary of Valuation Allowances Against Deferred Income Taxes (Detail) - USD ($)
$ in Thousands
Oct. 28, 2018
Apr. 29, 2018
Oct. 29, 2017
Valuation Allowance [Line Items]      
Valuation allowance $ 5,306 $ 5,204 $ 632
U.S. State Tax [Member] | Loss Carryforwards and Credits [Member]      
Valuation Allowance [Line Items]      
Valuation allowance 756 578 554
Internal Revenue Service (IRS) [Member] | Income Tax Credits [Member]      
Valuation Allowance [Line Items]      
Valuation allowance $ 4,550 4,550  
Poland [Member] | Loss Carryforwards [Member]      
Valuation Allowance [Line Items]      
Valuation allowance   $ 76 $ 78