Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 24, 2015	Jan. 25, 2014	Jan. 24, 2015	Jan. 25, 2014
Income Taxes
Effective tax rate (as a percent)	34.00%	33.30%	34.80%	33.50%
Statutory tax rate (as a percent)	35.00%		35.00%
Tax benefit from change in deferred tax assets valuation allowance		$ 0.2		$ 0.9
Effective tax rate before release of valuation allowance (as a percent)		34.00%		35.10%
Net liability for uncertain income tax positions	$ 1.1		$ 1.1