Fair Value Measurements - Hierarchy and Transfers (Details) - USD ($) $ in Thousands	Jan. 25, 2020	Apr. 27, 2019
Assets
Total assets	$ 50,814	$ 57,421
Recurring basis
Assets
Marketable securities	40,793	42,101
Held-to-maturity investments	3,542	3,341
Cost basis investments	6,479	11,979
Total assets	50,814	57,421
Liabilities
Contingent consideration liability	7,900	7,900
Recurring basis | Level 1
Assets
Marketable securities	4	5
Held-to-maturity investments	3,542	3,341
Total assets	3,546	3,346
Recurring basis | Level 2
Assets
Marketable securities	33,417	34,390
Total assets	33,417	34,390
Recurring basis | Level 3
Assets
Cost basis investments	6,479	11,979
Total assets	6,479	11,979
Liabilities
Contingent consideration liability	7,900	7,900
Recurring basis | NAV
Assets
Marketable securities	7,372	7,706
Total assets	$ 7,372	$ 7,706