Proton Solutions Loans and Investments - NYPC Loan (Details) - USD ($)	Jul. 31, 2015	Oct. 02, 2020	Sep. 27, 2019	May 01, 2019	Jun. 30, 2016
NYPC loan | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitment	$ 91,500,000
Long term notes		$ 34,900,000	$ 31,800,000
NYPC loan | Senior Subordinated Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitment	$ 18,500,000
Stated rate (as a percent)	13.50%			1000.00%
Long term notes		34,900,000
Financing Receivable, Term	6 years 6 months
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		20,000,000.0	16,600,000
Unbilled accounts receivable		$ 5,000,000.0	$ 6,000,000.0