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Significant Accounting Policies (Detail) - USD ($)
3 Months Ended 9 Months Ended
Jan. 28, 2018
Jan. 29, 2017
Jan. 28, 2018
Jan. 29, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Income taxes $ 8,208,000 $ 643,000 $ 11,956,000 $ 6,560,000
Accrued expenses and deferred compensation, operating activities     (1,608,000) (668,000)
Common stock surrendered for withholding taxes payable, financing activities     1,530,000 280,000
ASU No. 2016-09 [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Income taxes     $ (500,000)  
Excess tax benefit related to stock-based compensation, operating activities       195,000
Excess tax benefit related to stock-based compensation, financing activities       195,000
Accrued expenses and deferred compensation, operating activities       280,000
Common stock surrendered for withholding taxes payable, financing activities       $ 280,000