Intangible Assets and Goodwill - Narrative - Goodwill Impairment Test (Details) - USD ($) $ in Millions	12 Months Ended
	Apr. 28, 2018	Apr. 29, 2017	Apr. 30, 2016	May 02, 2015
Goodwill [Line Items]
Goodwill	$ 59.2	$ 1.6	$ 1.7	$ 1.7
Goodwill impairment charge	0.0	0.0	0.0
Interface
Goodwill [Line Items]
Goodwill	0.7	0.6	0.7	$ 0.7
Goodwill impairment charge	0.0	$ 0.0	$ 0.0
North American Automotive [Member]
Goodwill [Line Items]
Reporting Unit, Fair Value	708.5
Reporting Unit, Carrying Value	215.3
Reporting Unit, Amount of Fair Value in Excess of Carrying Amount	493.2
European Automotive [Member]
Goodwill [Line Items]
Reporting Unit, Fair Value	386.5
Reporting Unit, Carrying Value	302.1
Reporting Unit, Amount of Fair Value in Excess of Carrying Amount	84.4
Power Systems Group [Member]
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			135.00%
Reporting Unit, Fair Value	44.0
Reporting Unit, Carrying Value	13.1
Reporting Unit, Amount of Fair Value in Excess of Carrying Amount	30.9
Hetronic [Member]
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			163.00%
Reporting Unit, Fair Value	77.5
Reporting Unit, Carrying Value	32.0
Reporting Unit, Amount of Fair Value in Excess of Carrying Amount	$ 45.5