Proton Solutions Loans and Investments - APTC and RPTC Loans (Details) € in Millions, $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2017 USD ($)	Jul. 31, 2017 USD ($)	Jul. 31, 2017 EUR (€)	Oct. 02, 2020 USD ($)	Sep. 27, 2019 USD ($)	Sep. 28, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in available-for-sale securities				$ 0.0	$ 0.0	$ 17.8
Proton Center, Munich | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase of outstanding senior secured debt		$ 24.5	€ 21.5
RPTC securities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Claims filed against all of RPTC's assets | €			€ 77.0
APTC securities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investment in available-for-sale securities	$ 6.0
Stated rate (as a percent)				8.50%
Unbilled accounts receivable				$ 6.9	2.1
Long-term unbilled accounts receivable				5.7
RPTC securities
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled accounts receivable				$ 4.2	$ 4.6