Loans Receivable - Scheduled of loans receivable by property type (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Outstanding	$ 1,339.8	$ 1,504.1
Fair Value	$ 1,329.2	$ 1,492.6
Credit Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Fair Value	100.00%	100.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Outstanding	$ 867.4	$ 862.4
Fair Value	$ 858.1	$ 853.4
Office | Credit Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Fair Value	64.60%	57.20%
Apartments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Outstanding	$ 253.5	$ 253.3
Fair Value	$ 252.1	$ 252.0
Apartments | Credit Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Fair Value	19.00%	16.90%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Outstanding	$ 0.0	$ 161.4
Fair Value	$ 0.0	$ 161.3
Industrial | Credit Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Fair Value	0.00%	10.80%
Hotel
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Outstanding	$ 125.2	$ 125.3
Fair Value	$ 125.3	$ 125.3
Hotel | Credit Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Fair Value	9.40%	8.40%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Outstanding	$ 93.7	$ 101.7
Fair Value	$ 93.7	$ 100.6
Retail | Credit Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
% of Fair Value	7.00%	6.70%