Retirement and Welfare Plans - Non-qualified Plan (Details) - Non-qualified defined benefit retirement plan (not funded) - USD ($) $ in Millions	12 Months Ended
	Apr. 28, 2018	Apr. 29, 2017
Retirement and Welfare
Total cost recognized	$ 0.8	$ 0.9
Actuarial loss recognized in accumulated other comprehensive loss	0.2	0.2
Benefit payments	1.1	$ 1.1
Future benefit payments expected annually for the next ten years	$ 1.1
Discount rate used to determine benefit obligations (as a percent)	4.10%	3.90%
Other long-term liabilities
Retirement and Welfare
Plan obligations	$ 15.5	$ 16.7