Proton Solutions Loans and Investments - NYPC Loan (Details) - USD ($)	Jul. 31, 2015	Sep. 27, 2019	Sep. 28, 2018	Jun. 30, 2016
NYPC loan | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitment	$ 91,500,000
Long-term (1) (3)		$ 31,800,000	$ 28,000,000.0
NYPC loan | Senior Subordinated Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitment	$ 18,500,000
Term	6 years 6 months
Stated rate (as a percent)	13.50%
Long-term (1) (3)		31,800,000
Deutsche Bank | Senior First Lien Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitment				$ 73,000,000.0
New York Proton Center
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable		16,600,000
Unbilled accounts receivable		$ 6,000,000.0	$ 24,100,000