Fair Value Measurements - Hierarchy and Transfers (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 28, 2018	Apr. 29, 2017
Assets
Total assets	$ 59,354	$ 53,677
Recurring basis
Liabilities
Transfers from Level 1 to Level 2 assets	0	0
Transfers from Level 2 to Level 1 assets	0	0
Transfers into Level 3 assets	0	0
Transfers out of Level 3 assets	0	0
Transfers into Level 3 liabilities	0	0
Transfers out of Level 3 liabilities	0	0
Level 1 | Recurring basis
Assets
Total assets	4,481	3,083
Level 1 | Recurring basis | Available-for-sale investments
Assets
Total assets	1,141	1,217
Level 1 | Recurring basis | Held-to-maturity investments
Assets
Total assets	3,340	1,866
Level 2 | Recurring basis
Assets
Total assets	37,173	36,644
Level 2 | Recurring basis | Available-for-sale investments
Assets
Total assets	37,079	36,638
Level 2 | Recurring basis | Trading securities
Assets
Total assets	94	6
Level 3 | Recurring basis
Assets
Total assets	10,954	6,900
Liabilities
Contingent consideration liability	344	1,248
Level 3 | Recurring basis | Available-for-sale investments
Assets
Total assets		1,400
Level 3 | Recurring basis | Cost basis investments
Assets
Total assets	$ 10,954	$ 5,500