Fair Value Measurements (Details) - USD ($)	Apr. 30, 2016	Apr. 25, 2015
Assets
Transfers from Level 1 to Level 2	$ 0	$ 0
Transfers from Level 2 to Level 1	0	0
Level 1 | Recurring basis
Assets
Available-for-sale securities	1,452,000	1,552,000
Held-to-maturity investments	1,826,000
Total	3,278,000	1,552,000
Level 2 | Recurring basis
Assets
Available-for-sale securities	43,698,000	58,516,000
Trading securities		1,127,000
Total	$ 43,698,000	$ 59,643,000