Fair Value Measurements - Hierarchy and Transfers (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Oct. 29, 2016	Apr. 30, 2016
Assets
Total investments	$ 51,018	$ 46,976
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 investments	2,819	3,003
Level 1 | Recurring basis | Available-for-sale investments
Assets
Total investments	1,003	1,177
Level 1 | Recurring basis | Held-to-maturity investments
Assets
Total investments	1,816	1,826
Level 2 | Recurring basis
Assets
Total investments	34,342	36,802
Level 2 | Recurring basis | Available-for-sale investments
Assets
Total investments	33,908	$ 36,802
Level 2 | Recurring basis | Trading securities
Assets
Total investments	434
Level 3 | Recurring basis
Assets
Total investments	6,250
Liabilities
Contingent consideration liability	2,755
Level 3 | Recurring basis | Available-for-sale investments
Assets
Total investments	750
Level 3 | Recurring basis | Cost basis investment
Assets
Total investments	$ 5,500