Loans Receivable - Schedule of fair values and risk ratings (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($) loan	Dec. 31, 2021 USD ($) loan
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	28	31
Fair Value | $	$ 1,329.2	$ 1,492.6
Related Party
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans collateralized by equity interests in real estate investments	3	3
Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	100.00%	100.00%
AA
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	0	1
Fair Value | $	$ 0.0	$ 62.6
AA | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	4.20%
A
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2	4
Fair Value | $	$ 195.4	$ 248.5
A | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	14.70%	16.60%
A-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	1	0
Fair Value | $	$ 51.4	$ 0.0
A- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	3.90%	0.00%
BBB
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2	6
Fair Value | $	$ 102.1	$ 374.7
BBB | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	7.70%	25.10%
BBB-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	4	0
Fair Value | $	$ 117.3	$ 0.0
BBB- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	8.80%	0.00%
BB+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	5	0
Fair Value | $	$ 197.1	$ 0.0
BB+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	14.80%	0.00%
BB
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	3	10
Fair Value | $	$ 156.6	$ 437.8
BB | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	11.80%	29.30%
BB-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2	0
Fair Value | $	$ 129.1	$ 0.0
BB- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	9.70%	0.00%
B+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2	0
Fair Value | $	$ 74.7	$ 0.0
B+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	5.60%	0.00%
B
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2	5
Fair Value | $	$ 77.1	$ 144.3
B | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	5.80%	9.70%
C
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	2	2
Fair Value | $	$ 158.5	$ 154.8
C | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	11.90%	10.40%
NR
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans	3	3
Fair Value | $	$ 69.9	$ 69.9
NR | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	5.30%	4.70%