Retirement and Welfare, Defined Benefit and Defined Contribution (Details) (USD $)	12 Months Ended
	Apr. 25, 2015	Apr. 26, 2014	Apr. 27, 2013
Changes in plan assets and benefit obligations recognized in accumulated other comprehensive loss (pre-tax)
Beginning of year net actuarial loss	$ 39,425,000	$ 48,745,000
Net current year actuarial (gain) loss	836,000	(5,932,000)
Amortization of actuarial loss	(2,659,000)	(3,388,000)
End of year net actuarial loss	37,602,000	39,425,000	48,745,000
Unrecognized actuarial losses expected to be amortized in fiscal 2016	3,000,000
Components of net periodic pension cost and retirement costs
Other	124,000	223,000	191,000
Total retirement costs (excluding non-qualified defined benefit retirement plan)	11,536,000	11,189,000	8,114,000
401(k)
Components of net periodic pension cost and retirement costs
Defined contribution plan cost	6,270,000	5,802,000	5,198,000
PCRP
Components of net periodic pension cost and retirement costs
Defined contribution plan cost	1,377,000	2,513,000
Defined benefit pension plan for factory hourly employees
Components of net periodic pension cost and retirement costs
Service cost	1,114,000	1,241,000	1,231,000
Interest cost	5,070,000	4,822,000	5,325,000
Expected return on plan assets	(5,077,000)	(6,800,000)	(6,855,000)
Net amortization and deferral	2,658,000	3,388,000	3,024,000
Net periodic pension cost (hourly plan)	3,765,000	2,651,000	2,725,000
Change in benefit obligation
Benefit obligation at beginning of year	116,870,000	123,495,000
Service cost	1,114,000	1,241,000	1,231,000
Interest cost	5,070,000	4,822,000	5,325,000
Actuarial (gain) loss	3,664,000	(3,565,000)
Benefits paid	(5,638,000)	(9,123,000)
Benefit obligation at end of year	121,080,000	116,870,000	123,495,000
Change in plan assets
Fair value of plan assets at beginning of year	111,474,000	111,430,000
Actual return on plan assets	7,906,000	9,494,000
Other expenses		(327,000)
Benefits paid	(5,638,000)	(9,123,000)
Fair value of plan assets at end of year	113,742,000	111,474,000	111,430,000
Funded status	(7,338,000)	(5,396,000)
Other long-term liabilities	(7,338,000)	(5,396,000)
Actuarial assumptions for the defined benefit pension plan
Discount rate used to determine benefit obligations (as a percent)	4.20%	4.40%	4.00%
Discount rate used to determine net benefit cost (as a percent)	4.40%	4.00%	4.60%
Long-term rate of return (as a percent)	4.70%	4.70%	6.30%
Pension assets
Employer contributions	0
Expected contributions during fiscal 2016	7,000,000
Expected benefit payments
2016	6,195,000
2017	6,340,000
2018	6,504,000
2019	6,675,000
2020	6,856,000
2021 to 2025	36,373,000
Total	68,943,000
Defined benefit pension plan for factory hourly employees | Level 1
Change in plan assets
Fair value of plan assets at end of year	23,269,000	22,830,000
Defined benefit pension plan for factory hourly employees | Level 2
Change in plan assets
Fair value of plan assets at end of year	90,473,000	88,644,000
Defined benefit pension plan for factory hourly employees | Fixed rate investments
Pension assets
Strategic asset allocation (as a percent)	90.00%
Defined benefit pension plan for factory hourly employees | Cash and equivalents | Level 1
Change in plan assets
Fair value of plan assets at end of year	149,000	207,000
Defined benefit pension plan for factory hourly employees | Cash and equivalents | Level 2
Change in plan assets
Fair value of plan assets at end of year	3,685,000	6,083,000
Defined benefit pension plan for factory hourly employees | Equity funds | Level 1
Change in plan assets
Fair value of plan assets at end of year	23,120,000	22,623,000
Defined benefit pension plan for factory hourly employees | Equity funds | Level 2
Change in plan assets
Fair value of plan assets at end of year	7,702,000	7,736,000
Defined benefit pension plan for factory hourly employees | Debt funds | Level 2
Change in plan assets
Fair value of plan assets at end of year	$ 79,086,000	$ 74,825,000