Retirement and Welfare, Non-qualified Plan (Details) (USD $)	12 Months Ended
	Apr. 25, 2015	Apr. 26, 2014
Retirement and Welfare
Actuarial gain (loss) recognized in accumulated other comprehensive loss	$ (836,000)	$ 5,932,000
Non-qualified defined benefit retirement plan
Retirement and Welfare
Total cost recognized	800,000	800,000
Actuarial gain (loss) recognized in accumulated other comprehensive loss	(1,700,000)	400,000
Benefit payments	1,100,000	1,100,000
Future benefit payments expected annually for the next ten years	1,100,000
Discount rate used to determine benefit obligations (as a percent)	3.90%	4.30%
Non-qualified defined benefit retirement plan | Other long-term liabilities
Retirement and Welfare
Plan obligations	$ 17,500,000	$ 16,200,000