Secured Financing Agreements - Summary of Outstanding Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Repurchase facilities	$ 677,285	$ 1,708,875
Asset-specific financings	43,622	123,091
Term financing facility	127,145	0
Unused Capacity	1,122,715	616,125
Total Capacity	1,800,000	2,325,000
Carrying Value of Collateral	1,054,842	2,476,967
Goldman Sachs Bank USA
Line of Credit Facility [Line Items]
Term financing facility	127,145
Unused Capacity	0
Total Capacity	127,145
Goldman Sachs Bank USA | Revolving Credit Facility
Line of Credit Facility [Line Items]
Carrying Value of Collateral	$ 329,256
Weighted Average Borrowing Rate	3.70%
CIBC Bank USA
Line of Credit Facility [Line Items]
Asset-specific financings	$ 43,622	123,091
Unused Capacity	106,378	26,909
Total Capacity	150,000	150,000
CIBC Bank USA | Secured Debt
Line of Credit Facility [Line Items]
Carrying Value of Collateral	$ 56,129	$ 152,929
Weighted Average Borrowing Rate	1.80%	2.50%
Loans held-for-investment | Morgan Stanley Bank
Line of Credit Facility [Line Items]
Repurchase facilities	$ 230,982	$ 435,719
Unused Capacity	269,018	164,281
Total Capacity	500,000	600,000
Carrying Value of Collateral	$ 382,017	$ 657,066
Weighted Average Borrowing Rate	2.20%	2.30%
Maximum capacity under collateralized borrowings upon exercise of option to increase	$ 600,000
Loans held-for-investment | Goldman Sachs Bank USA
Line of Credit Facility [Line Items]
Repurchase facilities	81,227	$ 395,990
Unused Capacity	168,773	104,010
Total Capacity	250,000	500,000
Carrying Value of Collateral	$ 111,811	$ 593,625
Weighted Average Borrowing Rate	2.60%	2.50%
Maximum capacity under collateralized borrowings upon exercise of option to increase	$ 350,000
Loans held-for-investment | JPMorgan Chase Bank
Line of Credit Facility [Line Items]
Repurchase facilities	104,215	$ 361,797
Unused Capacity	345,785	88,203
Total Capacity	450,000	450,000
Carrying Value of Collateral	$ 188,838	$ 536,758
Weighted Average Borrowing Rate	2.30%	2.50%
Loans held-for-investment | Citibank
Line of Credit Facility [Line Items]
Repurchase facilities	$ 202,944	$ 386,049
Unused Capacity	297,056	113,951
Total Capacity	500,000	500,000
Carrying Value of Collateral	$ 285,767	$ 504,236
Weighted Average Borrowing Rate	1.80%	1.80%
Loans held-for-investment | Wells Fargo Bank
Line of Credit Facility [Line Items]
Repurchase facilities	$ 57,917	$ 129,320
Unused Capacity	42,083	145,680
Total Capacity	100,000	275,000
Carrying Value of Collateral	$ 86,409	$ 185,282
Weighted Average Borrowing Rate	2.30%	2.10%
Maximum capacity under collateralized borrowings upon exercise of option to increase	$ 200,000