Fair Value Measurements - Hierarchy and Transfers (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Oct. 27, 2018	Apr. 28, 2018
Assets
Total assets	$ 54,285	$ 59,354
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
Marketable securities	969	1,141
Held-to-maturity investments	3,218	3,340
Total assets	4,187	4,481
Level 2 | Recurring basis
Assets
Marketable securities	32,377	37,173
Total assets	32,377	37,173
Level 3 | Recurring basis
Assets
Cost basis investments	10,954	10,954
Total assets	10,954	10,954
Liabilities
Contingent consideration liability	$ 3,621	$ 344