Loans - Held for Investment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Investments in loans
Carrying Value	$ 19,627,876	$ 20,528,925
Face Amount	20,059,294	20,934,221
Credit loss allowances	(331,646)	(309,039)
Total net loans	$ 19,296,230	$ 20,219,886	$ 21,263,313	$ 21,186,033
Residential, fair value option
Investments in loans
Weighted Average Life	27 years 7 months 6 days	27 years 9 months 18 days
Commercial Portfolio Segment
Investments in loans
Carrying Value	$ 14,552,758
Credit loss allowances	(322,087)
Infrastructure Portfolio Segment
Investments in loans
Carrying Value	2,385,750
Credit loss allowances	(9,559)
Loans held for investment
Investments in loans
Carrying Value	16,938,508	$ 17,883,288
Face Amount	17,019,327	17,979,695
Credit loss allowances	(331,646)	(309,039)
Loans held for investment | Commercial Portfolio Segment
Investments in loans
Carrying Value	14,552,758	15,377,364
Face Amount	14,589,537	15,429,451
Credit loss allowances	(322,087)	(298,775)
Total net loans	14,230,671	15,078,589	16,094,593	16,048,507
Loans held for investment | Infrastructure Portfolio Segment
Investments in loans
Carrying Value	2,385,750	2,505,924
Face Amount	$ 2,429,790	$ 2,550,244
Weighted Average Life	3 years 8 months 12 days	3 years 10 months 24 days
Credit loss allowances	$ (9,559)	$ (10,264)
Total net loans	$ 2,376,191	$ 2,495,660	2,357,831	2,352,932
Loans held for investment | Weighted-average | Infrastructure Portfolio Segment
Investments in loans
Weighted Average Coupon	9.40%	9.50%
Loans under fair value option
Investments in loans
Carrying Value	$ 2,689,368	$ 2,645,637
Face Amount	3,039,967	2,954,526
Credit loss allowances	0
Total net loans	2,689,368	2,645,637	$ 2,810,889	$ 2,784,594
Loans under fair value option | Residential, fair value option
Investments in loans
Carrying Value	2,518,600	2,604,594
Face Amount	2,863,512	2,909,126
Loans under fair value option | Commercial, fair value option
Investments in loans
Carrying Value	123,619	41,043
Face Amount	$ 126,955	$ 45,400
Weighted Average Life	6 years 4 months 24 days	5 years 2 months 12 days
Loans under fair value option | Infrastructure Portfolio Segment
Investments in loans
Carrying Value	$ 47,149
Face Amount	49,500
Reclassification of loans	48,700
Fair value adjustment	$ 1,500
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	6.80%	5.50%
Loans under fair value option | Weighted-average | Infrastructure Portfolio Segment
Investments in loans
Weighted Average Coupon	11.50%
First Mortgages | Loans held for investment
Investments in loans
Carrying Value	$ 14,107,898	$ 14,956,646
Face Amount	$ 14,142,331	$ 15,005,827
Weighted Average Life	2 years 8 months 12 days	2 years 9 months 18 days
First Mortgages | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	9.00%	9.00%
Subordinated Mortgages | Loans held for investment
Investments in loans
Carrying Value	$ 77,495	$ 76,560
Face Amount	$ 77,619	$ 76,882
Weighted Average Life	2 years 1 month 6 days	2 years 2 months 12 days
Subordinated Mortgages | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	14.80%	14.80%
Mezzanine Loans
Investments in loans
Total net loans	$ 1,000,000	$ 1,000,000
Mezzanine Loans | Loans held for investment
Investments in loans
Carrying Value	296,699	273,146
Face Amount	$ 298,400	$ 274,899
Weighted Average Life	2 years 4 months 24 days	2 years 8 months 12 days
Mezzanine Loans | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	13.90%	13.70%
Other | Loans held for investment
Investments in loans
Carrying Value	$ 70,666	$ 71,012
Face Amount	$ 71,187	$ 71,843
Weighted Average Life	1 year 7 months 6 days	1 year 9 months 18 days
Other | Loans held for investment | Weighted-average
Investments in loans
Weighted Average Coupon	9.60%	9.60%