Income Taxes (Details) - USD ($)	3 Months Ended
	Jul. 29, 2017	Jul. 30, 2016
Income taxes
Benefit for income taxes	$ (3,180,000)	$ (3,863,000)
Effective tax benefit rate (as a percent)	41.60%	24.90%
Excess tax benefits	$ 1,025,000
Reversal of uncertain tax position reserve, including interest		$ 968,000