Commercial Mortgage Loans, Subordinate Loans and Other Lending Assets, Net - Allocation of Carrying Value of Loan Portfolio Based on Internal Risk Ratings (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($) loan
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	49	50
Total	$ 8,318,448	$ 8,384,575
Mortgage loans on real estate, commercial and consumer, percentage of portfolio	100.00%	100.00%
Year 1	$ 0	$ 440,720
Year 2	642,657	2,707,083
Year 3	2,744,155	2,285,902
Year 4	2,256,534	557,204
Year 5	417,696	1,597,927
Prior	2,257,406	795,739
General CECL Allowance	(32,558)	(26,482)
Carrying value, net	$ 8,285,890	$ 8,358,093
Weighted-Average Risk Rating	3.0	3.0
Gross write-offs	$ 0	$ 81,890
Off-balance-sheet, credit loss, liability, amount excluded	$ 3,600
1
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	0	0
Total	$ 0	$ 0
Mortgage loans on real estate, commercial and consumer, percentage of portfolio	0.00%	0.00%
Year 1	$ 0	$ 0
Year 2	0	0
Year 3	0	0
Year 4	0	0
Year 5	0	0
Prior	$ 0	$ 0
2
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	4	4
Total	$ 447,202	$ 478,440
Mortgage loans on real estate, commercial and consumer, percentage of portfolio	5.40%	5.70%
Year 1	$ 0	$ 0
Year 2	0	280,572
Year 3	332,059	0
Year 4	49,729	0
Year 5	0	132,309
Prior	$ 65,414	$ 65,560
3
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	41	42
Total	$ 7,658,452	$ 7,548,252
Mortgage loans on real estate, commercial and consumer, percentage of portfolio	92.10%	90.00%
Year 1	$ 0	$ 440,720
Year 2	642,657	2,426,511
Year 3	2,412,096	2,285,902
Year 4	2,206,805	387,323
Year 5	389,815	1,465,618
Prior	$ 2,007,079	$ 542,177
4
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	2	2
Total	$ 85,612	$ 88,112
Mortgage loans on real estate, commercial and consumer, percentage of portfolio	1.00%	1.10%
Year 1	$ 0	$ 0
Year 2	0	0
Year 3	0	0
Year 4	0	0
Year 5	0	0
Prior	$ 85,612	$ 88,112
5
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	2	2
Total	$ 127,182	$ 269,771
Mortgage loans on real estate, commercial and consumer, percentage of portfolio	1.50%	3.20%
Year 1	$ 0	$ 0
Year 2	0	0
Year 3	0	0
Year 4	0	169,881
Year 5	27,881	0
Prior	$ 99,301	$ 99,890

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