VPT Loans and Securities - CPTC Loans (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 29, 2017	Dec. 30, 2016	Sep. 29, 2017	Sep. 30, 2016	Oct. 02, 2015	Mar. 31, 2017	Jun. 30, 2014	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment charges			$ 51,400,000	$ 0	$ 0
Amortized cost	$ 59,800,000		59,800,000	95,300,000
Provision for doubtful accounts receivable		$ 37,800,000	43,700,000	3,500,000	$ 1,100,000
Allowance for doubtful accounts	63,100,000		63,100,000	24,200,000
Original CPTC Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	47,400,000		47,400,000	95,300,000
Original CPTC loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment charges	$ 13,100,000		$ 51,400,000
DIP Facility, amount of additional financing						$ 16,000,000
DIP Facility, interest rate (as a percent)	9.00%		9.00%
CPTC loan facility, amortization period over which monthly payments are calculated after January 1, 2015			15 years
Amount of amortizing principal payments to date			$ 0
Provision for doubtful accounts receivable		34,200,000
Allowance for doubtful accounts		34,200,000
Accounts receivable				32,600,000
Unbilled accounts receivable				$ 17,200,000
Original CPTC loans | LIBOR
Accounts, Notes, Loans and Financing Receivable [Line Items]
CPTC loan facility, interest rate margin (as a percent)	7.00%		7.00%
CPTC loan facility, minimum interest rate during initial term (as a percent)	9.00%		9.00%
Original CPTC loans | Tranche C Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum commitment	$ 9,700,000		$ 9,700,000
Original CPTC loans | Varian Medical Systems, Inc.
Accounts, Notes, Loans and Financing Receivable [Line Items]
DIP Facility, amount of additional financing						$ 7,300,000
DIP Facility, expected drawdown period (months)			12 months
Original CPTC loans | Varian Medical Systems, Inc. | Tranche C Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum commitment	4,400,000		$ 4,400,000
C P T C Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impairment charges		38,300,000
Amortized cost		60,000,000
Unbilled Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	$ 17,200,000		$ 17,200,000
Unbilled Receivables | Original CPTC loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for doubtful accounts receivable		$ 17,200,000
Available-for-sale Securities | Original CPTC loans | Tranche A loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum borrowing capacity								$ 165,300,000
Available-for-sale Securities | Original CPTC loans | Varian Medical Systems, Inc. | Tranche A loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum commitment							$ 70,300,000	$ 115,300,000
Significant sales							38,100,000
Available-for-sale Securities | Original CPTC loans | Varian Medical Systems, Inc. | Tranche B loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum commitment							10,000,000
Available-for-sale Securities | Original CPTC loans | J.P. Morgan | Tranche A loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sale of portion of commitment							$ 45,000,000