PROTON SOLUTIONS LOANS AND INVESTMENTS - Additional Information (Detail) € in Millions, $ in Millions			1 Months Ended					3 Months Ended	6 Months Ended		12 Months Ended	13 Months Ended
	Dec. 06, 2017 USD ($) tranche	Jul. 31, 2015 USD ($)	Sep. 28, 2018 USD ($)	Aug. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 31, 2017 USD ($)	Jul. 31, 2017 EUR (€)	Mar. 29, 2019 USD ($)	Mar. 29, 2019 USD ($)	Mar. 30, 2018 USD ($)	Sep. 29, 2017 USD ($)	Jul. 31, 2018 USD ($)	Jan. 01, 2023 USD ($)	Jan. 01, 2022 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)
Long term notes receivable and available for sale securities [Line Items]
Payments to acquire available-for-sale securities									$ 0.0	$ 6.0
Fair Value			$ 62.5					$ 65.0	65.0
Sale of available-for-sale security									0.0	8.0
Loss from equity investments									$ (2.2)	$ (0.9)
APTC Securities
Long term notes receivable and available for sale securities [Line Items]
Payments to acquire available-for-sale securities					$ 6.0
Interest rate (as a percent)								8.50%	8.50%
C P T C
Long term notes receivable and available for sale securities [Line Items]
Equity ownership interest (percent)	47.08%							47.08%	47.08%
Fair value of CPTC's equity	$ 20.1
Equity method investment	9.5		2.2					$ 0.0	$ 0.0
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, includes unbilled accounts receivable			4.5					4.5	4.5
Georgia Proton Therapy Center
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable			12.5					5.5	5.5
Unbilled receivables from variable interest entity			11.7					5.3	5.3
New York Proton Center
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable			24.1					24.0	24.0
MPTC loans (1)
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable			0.5					0.0	0.0
Cash received				$ 6.0
C P T C
Long term notes receivable and available for sale securities [Line Items]
Accounts receivable, includes unbilled accounts receivable			1.8					1.7	1.7
Impairment charges											$ 51.4
Liabilities assumed by lenders	112.0
Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Additional financing															$ 7.3
Loans Receivable | Proton Center, Munich
Long term notes receivable and available for sale securities [Line Items]
Payments to acquire outstanding senior debt						$ 24.5	€ 21.5
Loans Receivable | NYPC loan (1)
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment		$ 91.5
Loans Receivable | C P T C
Long term notes receivable and available for sale securities [Line Items]
Modified former loans receivable	$ 112.0
Revolving Loan | C P T C
Long term notes receivable and available for sale securities [Line Items]
Loans			3.7					4.7	4.7
Senior First Lien Loan | NYPC loan (1)
Long term notes receivable and available for sale securities [Line Items]
Maximum lending commitment																$ 73.0
Senior Subordinated Loans | NYPC loan (1)
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)		13.50%
Maximum lending commitment		$ 18.5
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			44.0					$ 44.0	$ 44.0
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]
Modified former loans receivable	$ 53.5
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	$ 2.0
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	7.2
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	15.6
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	$ 28.7
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]
Payments to acquire available-for-sale securities												$ 16.1
Interest rate (as a percent)							8.00%
Securities sold			8.5
Sale of available-for-sale security			$ 8.3
Available-for-sale Securities | MPTC Series B-1 Bonds [Member]
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)								7.50%	7.50%
Fair Value				25.0
Available-for-sale Securities | MPTC Series B-2 Bonds [Member]
Long term notes receivable and available for sale securities [Line Items]
Interest rate (as a percent)								8.50%	8.50%
Fair Value				$ 22.9
Forecast | Georgia Proton Therapy Center
Long term notes receivable and available for sale securities [Line Items]
Fair Value													$ 11.3
Forecast | Available-for-sale Securities | MPTC Series B-1 Bonds [Member]
Long term notes receivable and available for sale securities [Line Items]
Fair Value														$ 32.0
Forecast | Available-for-sale Securities | MPTC Series B-2 Bonds [Member]
Long term notes receivable and available for sale securities [Line Items]
Fair Value														$ 33.9
Revolving Loan | Loans Receivable | C P T C
Long term notes receivable and available for sale securities [Line Items]
Extension to the term (in years)									1 year
Maximum lending commitment									$ 15.0
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									$ 7.2
Other income (expense), net | Varian Medical Systems, Inc. | C P T C
Long term notes receivable and available for sale securities [Line Items]
Loss from equity investments								$ 0.0