DEBT - Narrative (Details)	Jun. 30, 2021 USD ($) extension	Sep. 30, 2021 USD ($)	Sep. 30, 2021 EUR (€)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 EUR (€)	Oct. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Short-term borrowing		$ 58,583,000		$ 52,200,000
Commercial Paper
Line of Credit Facility [Line Items]
Short-term borrowing		0		0
Short-term borrowing, maximum borrowing capacity						$ 30,000,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, number of extensions | extension	2
Line of credit facility, duration of extension (in years)	1 year
Line of credit facility, maximum borrowing capacity	$ 600,000,000
Line of credit facility, increase limit	$ 300,000,000
Compensating balance, amount		0
Revolving Credit Facility | United States
Line of Credit Facility [Line Items]
Short-term borrowing		47,000,000
Revolving Credit Facility | United Kingdom
Line of Credit Facility [Line Items]
Short-term borrowing		11,600,000	€ 10,000,000
Prior Credit Facility
Line of Credit Facility [Line Items]
Short-term borrowing				52,000,000	€ 0
Senior unsecured debts 1.26% USD floating swapped to 1.36% EUR fixed, due in 2022
Line of Credit Facility [Line Items]
Remaining outstanding under the amended term facility		$ 56,000,000		$ 112,000,000