Variable Interest Entities and Collateralized Loan Obligations - Additional Information (Details)			3 Months Ended		6 Months Ended
	Jun. 15, 2021	Mar. 31, 2021 USD ($) Loan Participation $ / shares shares	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) Loan	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Aggregate principal balance			$ 863,751,000		$ 863,751,000		$ 1,524,175,000
FL3 Mortgage Assets
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Principal amount of mortgage assets issued			5,800,000		163,100,000
Net cash proceeds utilizing replenishment feature			2,000,000.0		49,300,000
Repayment of existing borrowings including accrued interest			3,800,000		113,800,000
Aggregate principal balance			$ 1,200,000,000		$ 1,200,000,000
Loans held for investment, aggregate unpaid principal balance percentage			25.40%		25.40%
FL2-Notes
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Aggregate principal balance			$ 964,500,000		$ 964,500,000
Loans held for investment, aggregate unpaid principal balance percentage			20.00%		20.00%
FL3-Notes | Collateralized Loan Obligation Proceeds Held at Trustee
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Cash available to acquire eligible assets					$ 1,200,000
Collateralized Loan Obligation
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Number of mortgage loans originated or acquired | Loan					3
Principal amount of mortgage assets issued					$ 3,400,000,000
Percentage of loan investment portfolio collateralized			70.20%		70.20%
Unamortized issuance costs			$ 14,654,000		$ 14,654,000		$ 9,192,000
Collateralized Loan Obligation | FL2-Notes
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Principal amount of mortgage assets issued				$ 58,800,000		$ 133,000,000.0
Net cash proceeds utilizing replenishment feature				20,500,000		65,600,000
Repayment of existing borrowings including accrued interest			32,200,000	38,300,000	36,400,000	67,400,000
Collateralized Loan Obligation | FL4 Notes
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Notes issued		$ 1,250,000,000
Preferred stock, shares issued | shares		112,500
Preferred stock, par value | $ / shares		$ 0.001
Derivative, notional amount		$ 1,000,000
Issuance costs incurred					8,300,000
Unamortized issuance costs			7,800,000		7,800,000
Interest expense excluding amortization of deferred financing costs			4,600,000		4,700,000
Collateralized Loan Obligation | FL4 Investment Grade Rated Notes
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Notes issued		1,040,000,000.00
Collateralized Loan Obligation | FL4 Securities
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Principal amount of mortgage assets issued					77,200,000
Amount used to purchase eligible collateral interests		$ 308,900,000
Ramp-up period		6 months
Cash distributed for investment or other corporate uses		$ 104,800,000
Number of commercial real estate whole loan | Loan		1
Number of pari passu participations | Participation		17
Number of separate commercial real estate whole loans | Loan		17
Debt securities			308,900,000		308,900,000
Net cash proceeds utilizing replenishment feature					15,500,000
Repayment of existing borrowings including accrued interest					23,500,000
Aggregate principal balance			$ 1,200,000,000		$ 1,200,000,000
Loans held for investment, aggregate unpaid principal balance percentage			24.80%		24.80%
Cash available to acquire eligible assets					$ 52,600,000
Collateralized Loan Obligation | FL3-Notes
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Interest expense excluding amortization of deferred financing costs			$ 3,800,000	4,800,000	7,600,000	12,100,000
Debt issuance costs, gross			7,800,000		7,800,000
Unamortized issuance costs			3,900,000		$ 3,900,000
Collateralized Loan Obligation | FL3-Notes | Secured Overnight Financing Rate
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Line of credit, spread on variable rate	0.11448%
Interest rate terms					interest accrual period shall be the “30-Day Average SOFR” published on the website of the Federal Reserve Bank of New York on each benchmark determination date. SOFR will be determined by the calculation agent in arrears using a lookback period equal to the number of calendar days in such interest accrual period plus two SOFR Business Days.
Collateralized Loan Obligation | FL2-Notes
Variable Interest Entities And Collateralized Loan Obligation [Line Items]
Interest expense excluding amortization of deferred financing costs			3,100,000	$ 4,000,000.0	$ 6,200,000	$ 10,000,000.0
Debt issuance costs, gross			8,700,000		8,700,000
Unamortized issuance costs			$ 2,600,000		$ 2,600,000