Mortgage Debt - Schedule of Mortgage Debt (Details) - Mortgage debt - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	$ 2,901.8	$ 3,034.5
Unamortized loan fees	(14.8)	(16.5)
Total debt	2,887.0	3,018.0
Unamortized discount (premium)	(0.8)	(0.6)
Mortgage Loans Secured by Multi-Family Properties \| Western U.S.
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	1,659.4	1,692.9
Mortgage Loans Secured by Commercial \| Western U.S.
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	268.7	296.6
Mortgage Loans Secured by Commercial \| United Kingdom
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	558.0	637.4
Mortgage Loans Secured by Commercial \| Ireland
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	378.2	370.7
Mortgage Loans Secured by Commercial \| Spain
Debt Instrument [Line Items]
Mortgage debt (excluding loan fees)	$ 37.5	$ 36.9

Long-Term Debt, Net of (Premium) Discount

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Amount, after accumulated amortization, of debt discount (premium).

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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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