Convertible Senior Notes - Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Dec. 30, 2017	Dec. 30, 2017	Dec. 31, 2016	Mar. 31, 2017
Debt Instrument [Line Items]
Amortization of the debt discount		$ 8.2	$ 0.0
Convertible Debt | Convertible Senior Notes Due 2024
Debt Instrument [Line Items]
Contractual interest expense	$ 0.3	0.6
Amortization of the debt discount	4.1	8.2
Total interest expense	$ 4.4	$ 8.8
Effective interest rate on the liability component	5.40%	5.40%		5.40%