Fair Value Measurements - Hierarchy and Transfers (Details) - USD ($) $ in Thousands	Oct. 26, 2019	Apr. 27, 2019
Assets
Total assets	$ 59,510	$ 57,421
Recurring basis
Assets
Marketable securities	43,461	42,101
Held-to-maturity investments	3,570	3,341
Cost basis investments	12,479	11,979
Total assets	59,510	57,421
Liabilities
Contingent consideration liability	7,900	7,900
Recurring basis | Level 1
Assets
Marketable securities	4	5
Held-to-maturity investments	3,570	3,341
Total assets	3,574	3,346
Recurring basis | Level 2
Assets
Marketable securities	35,862	34,390
Total assets	35,862	34,390
Recurring basis | Level 3
Assets
Cost basis investments	12,479	11,979
Total assets	12,479	11,979
Liabilities
Contingent consideration liability	7,900	7,900
Recurring basis | NAV
Assets
Marketable securities	7,595	7,706
Total assets	$ 7,595	$ 7,706