Loans Receivable - Schedule of fair values and risk ratings (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	34	35
Fair Value | $	$ 1,365.5	$ 1,488.6
Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	100.00%	100.00%
A+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	1
Fair Value | $	$ 0.0	$ 0.0
A+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	0.00%
A
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	2
Fair Value | $	$ 0.0	$ 130.6
A | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	8.80%
A-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	1
Fair Value | $	$ 0.0	$ 0.0
A- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	0.00%
BBB+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	3
Fair Value | $	$ 0.0	$ 191.0
BBB+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	12.80%
BBB
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	2	2
Fair Value | $	$ 200.7	$ 137.4
BBB | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	14.70%	9.20%
BBB-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	1
Fair Value | $	$ 0.0	$ 47.5
BBB- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	3.20%
BB+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	5	2
Fair Value | $	$ 282.3	$ 64.9
BB+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	20.70%	4.40%
BB
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	1	2
Fair Value | $	$ 57.3	$ 72.3
BB | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	4.20%	4.80%
BB-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	1
Fair Value | $	$ 0.0	$ 18.9
BB- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	1.30%
B+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	3	3
Fair Value | $	$ 119.3	$ 87.2
B+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	8.70%	5.90%
B
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	1	2
Fair Value | $	$ 71.6	$ 72.5
B | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	5.20%	4.90%
B-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	6	5
Fair Value | $	$ 320.2	$ 171.0
B- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	23.50%	11.50%
CCC+
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	3
Fair Value | $	$ 0.0	$ 223.4
CCC+ | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	15.00%
CCC-
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	0	2
Fair Value | $	$ 0.0	$ 60.9
CCC- | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.00%	4.10%
CC
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	1	1
Fair Value | $	$ 12.8	$ 66.0
CC | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	0.90%	4.40%
C
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	4	1
Fair Value | $	$ 156.4	$ 75.1
C | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	11.50%	5.00%
D
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	6	0
Fair Value | $	$ 43.9	$ 0.0
D | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	3.20%	0.00%
NR
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans | loan	5	3
Fair Value | $	$ 101.0	$ 69.9
NR | Loans Receivable | Credit Concentration Risk
Financing Receivable, Credit Quality Indicator [Line Items]
% of Fair Value	7.40%	4.70%