Loans - Held for Investment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Investments in loans
Carrying Value	$ 20,107,790	$ 21,285,446
Face Amount	20,696,679	21,734,785
Credit loss allowances	(271,320)	(99,413)
Total net loans	$ 19,836,470	$ 21,186,033	$ 20,309,506	$ 18,413,649
Residential, fair value option
Investments in loans
Weighted Average Life	28 years	28 years 9 months 18 days
Commercial Portfolio Segment
Investments in loans
Carrying Value	$ 15,221,801
Credit loss allowances	(261,914)
Infrastructure Portfolio Segment
Investments in loans
Carrying Value	2,283,724
Credit loss allowances	(9,406)
Loans held for investment
Investments in loans
Carrying Value	17,505,525	$ 18,500,852
Face Amount	17,634,146	18,617,970
Credit loss allowances	(271,320)	(99,413)
Loans held for investment | Commercial Portfolio Segment
Investments in loans
Carrying Value	15,221,801	16,137,308
Face Amount	15,299,674	16,222,208
Credit loss allowances	(261,914)	(88,801)
Total net loans	14,959,887	16,048,507	15,676,202	13,450,198
Loans held for investment | Infrastructure Portfolio Segment
Investments in loans
Carrying Value	2,283,724	2,363,544
Face Amount	$ 2,334,472	$ 2,395,762
Weighted Average Life	4 years	3 years 10 months 24 days
Credit loss allowances	$ (9,406)	$ (10,612)
Total net loans	$ 2,274,318	$ 2,352,932	2,374,444	2,027,426
Loans held for investment | Weighted-average | Infrastructure Portfolio Segment
Investments in loans
Weighted Average Coupon	9.60%	8.60%
Loans under fair value option
Investments in loans
Carrying Value	$ 2,602,265	$ 2,784,594
Face Amount	3,062,533	3,116,815
Credit loss allowances	0
Total net loans	2,602,265	2,784,594	$ 2,205,684	$ 2,876,800
Loans under fair value option | Residential, fair value option
Investments in loans
Carrying Value	2,499,681	2,763,458
Face Amount	2,954,536	3,092,915
Loans under fair value option | Commercial, fair value option
Investments in loans
Carrying Value	102,584	21,136
Face Amount	$ 107,997	$ 23,900
Weighted Average Life	6 years 1 month 6 days	8 years 7 months 6 days
Loans under fair value option | Weighted-average | Residential, fair value option
Investments in loans
Weighted Average Coupon	4.50%	4.50%
Loans under fair value option | Weighted-average | Commercial, fair value option
Investments in loans
Weighted Average Coupon	7.00%	5.70%
First Mortgages | Loans held for investment
Investments in loans
Carrying Value	$ 14,812,543	$ 15,562,452
Face Amount	$ 14,887,200	$ 15,648,358
Weighted Average Life	1 year 3 months 18 days	1 year 8 months 12 days
First Mortgages | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	9.00%	7.90%
Subordinated Mortgages | Loans held for investment
Investments in loans
Carrying Value	$ 75,097	$ 71,100
Face Amount	$ 75,617	$ 72,118
Weighted Average Life	1 year 1 month 6 days	1 year 9 months 18 days
Subordinated Mortgages | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	14.80%	13.60%
Mezzanine Loans
Investments in loans
Total net loans	$ 1,100,000	$ 1,300,000
Mezzanine Loans | Loans held for investment
Investments in loans
Carrying Value	246,968	445,363
Face Amount	$ 248,518	$ 442,339
Weighted Average Life	1 year 7 months 6 days	1 year
Mezzanine Loans | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	13.50%	12.90%
Other | Loans held for investment
Investments in loans
Carrying Value	$ 87,193	$ 58,393
Face Amount	$ 88,339	$ 59,393
Weighted Average Life	1 year 7 months 6 days	1 year 4 months 24 days
Other | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	9.60%	8.20%