Commercial Mortgage Loans, Held for Investment - Schedule of Commercial Mortgage Loans, Held for Investment Portfolio (Details) - Commercial Mortgage Receivable, Held-For-Investment - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 4,051,936	$ 4,435,511
Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	100.00%	100.00%
Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	100.00%	100.00%
Southeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 1,754,872	$ 1,832,831
Southeast \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	43.30%	41.40%
Southwest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 1,120,991	$ 1,431,471
Southwest \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	27.60%	32.30%
Mideast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 364,039	$ 348,750
Mideast \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	9.00%	7.90%
Far West
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 158,184	$ 239,874
Far West \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	3.90%	5.40%
New England
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 137,211	$ 125,982
New England \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	3.40%	2.80%
Great Lakes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 105,315	$ 108,095
Great Lakes \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	2.60%	2.40%
Rocky Mountain
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 113,030	$ 76,180
Rocky Mountain \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	2.80%	1.70%
Various
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 298,294	$ 272,328
Various \| Geographic Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	7.40%	6.10%
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 3,354,417	$ 3,434,672
Multifamily \| Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	82.80%	77.50%
Hospitality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 361,375	$ 515,144
Hospitality \| Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	8.90%	11.60%
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 181,495	$ 309,522
Industrial \| Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	4.50%	7.00%
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 35,867	$ 58,259
Office \| Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	0.90%	1.30%
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 0	$ 1,986
Retail \| Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	0.00%	0.00%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 118,782	$ 115,928
Other \| Customer Concentration Risk \| Commercial mortgage loans, held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage	2.90%	2.60%

Commercial Mortgage Loans, Held for Investment - Schedule of Commercial Mortgage Loans, Held for Investment Portfolio (Details) - Commercial Mortgage Receivable, Held-For-Investment - USD ($)
$ in Thousands