VPT LOANS AND INVESTMENT - Additional Information (Detail) € in Millions			1 Months Ended			3 Months Ended			6 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 (€)	Mar. 30, 2018 USD ($) board_seat	Sep. 29, 2017 USD ($)	Mar. 31, 2017 USD ($)	Mar. 30, 2018 USD ($) board_seat	Mar. 31, 2017 USD ($)	Nov. 30, 2015 USD ($)	Jan. 01, 2023 USD ($)	Dec. 03, 2017 USD ($)	Jul. 31, 2017 EUR (€)	Apr. 30, 2017 USD ($)	Dec. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	May 31, 2015 USD ($) installment
Long term notes receivable and available for sale securities [Line Items]
Commitment						$ 10,700,000	$ 60,100,000		$ 10,700,000
Impairment charges						11,100,000		$ 0	11,100,000	$ 38,300,000
Payments to acquire available-for-sale securities									6,000,000	1,100,000
Sale of available-for-sale securities									8,000,000	0
Principal payments on notes receivable									5,200,000	$ 0
Available-for-sale securities:						10,700,000	60,100,000		10,700,000
APTC Securities
Long term notes receivable and available for sale securities [Line Items]
Commitment						$ 6,100,000	0		$ 6,100,000				$ 6,000,000
Interest rate (as a percent)						8.50%			8.50%
DRTC securities (4)
Long term notes receivable and available for sale securities [Line Items]
Commitment						$ 0	8,300,000		$ 0						$ 8,000,000
Sale of available-for-sale securities			$ 8,500,000
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		0
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		$ 9,500,000
Number of CPTC board seats held by the Company | board_seat						1			1
Number of CPTC board seats | board_seat						5			5
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, includes unbilled accounts receivable						$ 4,500,000	4,500,000		$ 4,500,000
Georgia Proton Therapy Center
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable						6,400,000	0		6,400,000
Unbilled receivables from variable interest entity						6,200,000			6,200,000
New York Proton Center [Member]
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable						13,800,000	13,300,000		13,800,000
Unbilled receivables from variable interest entity						13,800,000	1,300,000		13,800,000
MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable						$ 0	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%			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%			47.08%
Fair value of CPTC's equity						$ 20,100,000			$ 20,100,000
Equity method investment						9,500,000			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
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 | RPTC Securities
Long term notes receivable and available for sale securities [Line Items]
Short-term						26,400,000	25,400,000		26,400,000
Loans Receivable | PI loan (3)
Long term notes receivable and available for sale securities [Line Items]
Long-term						2,600,000	3,100,000		2,600,000
Loans Receivable | NYPC loan (3)
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment		$ 91,500,000
Long-term						$ 26,200,000	24,600,000		$ 26,200,000
Loans Receivable | MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)						12.00%			12.00%
Impairment charges						$ 11,100,000
Maximum lending commitment																		$ 35,000,000
Number of annual payments | installment																		3
Notes receivable						58,900,000	67,400,000		$ 58,900,000
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]
Deferral						25,100,000.0			25,100,000.0
Loans Receivable | Other Assets | MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Long-term						33,800,000	42,300,000		33,800,000
Loans Receivable | Prepaid expenses and other current assets [Member] | MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Short-term						25,100,000			25,100,000
Notes receivable							25,100,000
Revolving Loan | C P T C
Long term notes receivable and available for sale securities [Line Items]
Loans						3,100,000	0		3,100,000
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]
Modified former loans receivable						44,000,000	$ 0		44,000,000
Cost basis of term loan receivable						$ 53,500,000			$ 53,500,000
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]
Modified former loans receivable	$ 53,500,000
Number of Tranches | tranche	4
Paid-in-kind interest receivable (percent)						7.50%			7.50%
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche A loan
Long term notes receivable and available for sale securities [Line Items]
Modified former loans receivable	$ 2,000,000
Interest receivable, default rate (percent)									9.50%
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche B loan
Long term notes receivable and available for sale securities [Line Items]
Modified former loans receivable	7,200,000
Paid-in-kind interest receivable (percent)						10.00%			10.00%
Interest receivable, default rate (percent)									12.00%
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche C Loans
Long term notes receivable and available for sale securities [Line Items]
Modified former loans receivable	15,600,000
Interest receivable, default rate (percent)									9.50%
Term Loan | Varian Medical Systems, Inc. | C P T C | Tranche D Loans
Long term notes receivable and available for sale securities [Line Items]
Modified former loans receivable	$ 28,700,000
Interest receivable, default rate (percent)									9.50%
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
Selling, general and administrative expenses | Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Income (Loss) on equity investment in affiliate						$ (900,000)