VPT LOANS AND INVESTMENT - Additional Information (Detail) € in Millions			1 Months Ended			3 Months Ended			51 Months Ended
	Dec. 06, 2017 USD ($) tranche	Jul. 31, 2015 USD ($)	Jan. 31, 2018 USD ($)	Jul. 31, 2017 USD ($)	Jul. 31, 2017 EUR (€)	Dec. 29, 2017 USD ($)	Sep. 29, 2017 USD ($)	Dec. 30, 2016 USD ($)	Nov. 30, 2015 USD ($)	Jan. 01, 2023 USD ($)	Jul. 31, 2017 EUR (€)	Apr. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	May 31, 2015 USD ($) installment
Long term notes receivable and available for sale securities [Line Items]
Commitment						$ 18,500,000	$ 59,800,000
Payments to acquire available-for-sale securities						6,000,000		$ 600,000
Principal payments on notes receivable						500,000		0
Available-for-sale securities:						18,500,000	59,800,000
APTC Securities
Long term notes receivable and available for sale securities [Line Items]
Commitment						$ 6,000,000	0
Interest rate (as a percent)						8.50%
DRTC securities (4)
Long term notes receivable and available for sale securities [Line Items]
Commitment						$ 8,000,000	8,000,000
DRTC Securities
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)												8.50%
Original CPTC loans
Long term notes receivable and available for sale securities [Line Items]
Commitment						0	47,400,000
Impairment charges								38,300,000
Available-for-sale securities:								$ 60,000,000
C P T C
Long term notes receivable and available for sale securities [Line Items]
Equity method investment						9,500,000	0
RPTC Securities
Long term notes receivable and available for sale securities [Line Items]
Claims Filed Against Assets of Company in Bankruptcy | €											€ 89.0
Accounts receivable from CPTC, includes unbilled accounts receivable						4,500,000	4,500,000
NYPC loan (3)
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable from CPTC, includes unbilled accounts receivable						7,900,000	13,300,000
Unbilled receivables from variable interest entity						7,900,000	1,300,000
MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable from CPTC, includes unbilled accounts receivable						$ 0	0
C P T C
Long term notes receivable and available for sale securities [Line Items]
Impairment charges							13,100,000
Liabilities assumed by lenders	$ 112,000,000
Additional financing							16,000,000.0
Interest rate						9.00%
Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Ownership interest in dpiX Holding LLC (as a percent)						47.08%
Fair value of equity method investment						$ 9,500,000
Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Additional financing							7,300,000
C P T C
Long term notes receivable and available for sale securities [Line Items]
Fair value of CPTC's equity						20,100,000
Subordinated Bond | PI loan (3) | DRTC securities (4)
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)												8.50%
Long-term												$ 3,000,000
Principal payments on notes receivable						500,000
Subordinated Bond | PI loan (3) | Public Finance Authority | DRTC securities (4)
Long term notes receivable and available for sale securities [Line Items]
Commitment												$ 3,000,000
Loans Receivable | Proton Center, Munich
Long term notes receivable and available for sale securities [Line Items]
Payments to Acquire Senior Secured Debt				$ 24,500,000	€ 21.5
Loans Receivable | PI loan (3)
Long term notes receivable and available for sale securities [Line Items]
Long-term						2,500,000	3,000,000
Loans Receivable | NYPC loan (3)
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment		$ 91,500,000
Long-term						$ 18,500,000	18,500,000
Loans Receivable | MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)						12.00%
Maximum lending commitment														$ 35,000,000
Number of annual payments | installment														3
Loans Receivable | C P T C
Long term notes receivable and available for sale securities [Line Items]
Modified former loans receivable	$ 112,000,000
Loans Receivable | Reclassification From Long-Term Notes Receivable | MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)						15.00%
Long-term						$ 25,100,000
Deferral						25,100,000.0
Senior First Lien Loan | NYPC loan (3)
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment													$ 73,000,000
Senior Subordinated Loans | NYPC loan (3)
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)		13.50%
Maximum lending commitment		$ 18,500,000
Term (in years)		6 years 6 months
Term Loan | C P T C
Long term notes receivable and available for sale securities [Line Items]
Cost basis of term loan receivable						53,500,000
Modified former loans receivable						$ 44,000,000	$ 0
Term Loan | C P T C
Long term notes receivable and available for sale securities [Line Items]
Credit facility term (in years)	3 years
Term Loan | Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Paid-in-kind interest receivable (percent)						7.50%
Modified former loans receivable	$ 53,500,000
Number of Tranches | tranche	4
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche A loan
Long term notes receivable and available for sale securities [Line Items]
Interest receivable, default rate (percent)						9.50%
Modified former loans receivable	$ 2,000,000
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche B loan
Long term notes receivable and available for sale securities [Line Items]
Paid-in-kind interest receivable (percent)						10.00%
Interest receivable, default rate (percent)						12.00%
Modified former loans receivable	7,200,000
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche C Loans
Long term notes receivable and available for sale securities [Line Items]
Interest receivable, default rate (percent)						9.50%
Modified former loans receivable	15,600,000
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche D Loans
Long term notes receivable and available for sale securities [Line Items]
Interest receivable, default rate (percent)						9.50%
Modified former loans receivable	$ 28,700,000
Available-for-sale Securities | Georgia Proton Therapy Center
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)				8.00%							8.00%
Maximum lending commitment				$ 16,100,000
Payments to acquire available-for-sale securities				$ 4,300,000
Available-for-sale Securities | C P T C
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment									$ 185,000,000
Available-for-sale Securities | Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment									$ 84,700,000
Forecast | Available-for-sale Securities | Georgia Proton Therapy Center
Long term notes receivable and available for sale securities [Line Items]
Available-for-sale Securities, Debt Securities										$ 6,600,000
Revolving Loan | Loans Receivable | C P T C
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment						$ 15,000,000
Credit facility term (in years)						1 year
Revolving Loan | Loans Receivable | Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment						$ 7,200,000
Loans						$ 2,400,000
Subsequent Event | DRTC securities (4)
Long term notes receivable and available for sale securities [Line Items]
Proceeds from sale of subordinate bonds, including accrued interest			$ 8,500,000