MORTGAGE DEBT - Schedule of Mortgage Debt (Details) - Mortgage debt - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Debt (excluding loan fees)	$ 3,034.5	$ 2,977.6
Unamortized loan fees	(16.5)	(17.8)
Total debt	3,018.0	2,959.8
Unamortized premium (discount)	(0.6)	2.5
Mortgage Loans Secured by Multi-Family Properties \| Western U.S.
Debt Instrument [Line Items]
Debt (excluding loan fees)	1,692.9	1,493.1
Mortgage Loans Secured by Commercial \| Western U.S.
Debt Instrument [Line Items]
Debt (excluding loan fees)	296.6	351.0
Mortgage Loans Secured by Commercial \| United Kingdom
Debt Instrument [Line Items]
Debt (excluding loan fees)	637.4	683.8
Mortgage Loans Secured by Commercial \| Ireland
Debt Instrument [Line Items]
Debt (excluding loan fees)	370.7	327.3
Mortgage Loans Secured by Commercial \| Spain
Debt Instrument [Line Items]
Debt (excluding loan fees)	$ 36.9	40.4
Mortgage Loans Secured by Hotel \| Ireland
Debt Instrument [Line Items]
Debt (excluding loan fees)		$ 82.0

Long-Term Debt, Net of (Premium) Discount

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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