LONG-TERM DEBT - Schedule of Long-Term Debt (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	$ 2,008,500,000	$ 2,676,600,000
Long-term Debt and Lease Obligation, Current	117,500,000	103,100,000
Unamortized Debt Issuance Expense	12,300,000	14,200,000
Long-term Debt and Lease Obligation	1,878,700,000	2,559,300,000
Line of credit | Senior Credit Facility Due June Twenty Twenty Two [Member]
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	527,600,000	758,700,000
Maximum borrowing capacity of line of credit facility	1,200,000,000
Term Loan | Term Loan Facility Due Twenty Twenty Two [Member]
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	767,700,000	1,172,200,000
Maximum borrowing capacity of line of credit facility	1,300,000,000
Senior Notes | Senior Notes Facility Due 2024
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	600,000,000.0	600,000,000.0
Unamortized Debt Issuance Expense			$ 7,100,000
Maximum borrowing capacity of line of credit facility	600,000,000
Promissory notes and deferred consideration | Notes Weighted Average Maturity Two Point Three Years And Two Point Five Years [Member]
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	$ 49,800,000	$ 73,100,000
Long-term debt, maturity	2 years 1 month 6 days	2 years 6 months
Foreign bank debt | 1.4 years and 1.6 years
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	$ 36,700,000	$ 42,200,000
Long-term debt, maturity	1 year 2 months 12 days	1 year 7 months 6 days
Obligations under finance leases
Debt Instrument [Line Items]
Long-term Debt and Lease Obligation, Including Current Maturities	$ 26,700,000	$ 30,400,000