Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 26, 2013	Jan. 28, 2012	Jan. 26, 2013	Jan. 28, 2012
Income Taxes [Abstract]
Effective tax rate (in hundredths)	33.30%	15.70%	34.60%	(102.20%)
Impact of effective tax rate due to discrete items	$ 1.1		$ 1.1
Non-taxable book gain on sale of investments	1.0		1.0
Reduction of effective tax rate due to other discrete items (in hundredths)		19.40%
Impact of adjusting the valuation allowance on certain deferred tax assets		2.8
Impact of adjusting the valuation allowance on other discrete items		0.8
Effective income tax rate before adjustments (in hundredths)	37.70%	35.10%	37.20%	35.50%
Liability for uncertain tax positions	$ 1.4		$ 1.4