Fair Value of Financial Instruments - Carrying Value and Estimated Fair Value of Company's Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participations sold	$ (26,948)	$ (34,974)
Commercial Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participations sold	(26,948)	(9,217)
Subordinate Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participations sold	0	(25,757)
Carrying Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash and cash equivalents	243,414	325,498
Carrying Value \| Level III
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subordinate loan, held for sale	41,773	0
Secured debt arrangements, net	(3,439,302)	(3,436,672)
Participations sold	(26,948)	(34,974)
Debt related To real estate owned, held for sale	0	(33,000)
Carrying Value \| Level III \| Secured Debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Senior secured term loans, net	(773,397)	(483,465)
Carrying Value \| Level III \| Senior Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Senior secured term loans, net	(493,893)	0
Carrying Value \| Level III \| 2022 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(342,414)	(340,361)
Carrying Value \| Level III \| 2023 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(226,460)	(225,293)
Carrying Value \| Level III \| Commercial Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,397,772	5,451,084
Carrying Value \| Level III \| Subordinate Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	817,759	1,045,893
Estimate of Fair Value Measurement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash and cash equivalents	243,414	325,498
Estimate of Fair Value Measurement \| Level III
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subordinate loan, held for sale	42,001	0
Secured debt arrangements, net	(3,439,302)	(3,436,672)
Participations sold	(26,929)	(34,919)
Debt related To real estate owned, held for sale	0	(33,000)
Estimate of Fair Value Measurement \| Level III \| Secured Debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Senior secured term loans, net	(779,410)	(475,263)
Estimate of Fair Value Measurement \| Level III \| Senior Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Senior secured term loans, net	(486,005)	0
Estimate of Fair Value Measurement \| Level III \| 2022 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(345,511)	(327,381)
Estimate of Fair Value Measurement \| Level III \| 2023 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(234,600)	(214,875)
Estimate of Fair Value Measurement \| Level III \| Commercial Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,283,550	5,361,948
Estimate of Fair Value Measurement \| Level III \| Subordinate Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 705,683	$ 1,027,582

Debt Related To Real Estate Owned, Held For Sale

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- Definition

Real Estate Owned, Subordinate Loans, Held For Sale, Net

+ References

No definition available.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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- Definition

Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

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- Definition

Fair value portion of mortgage loans held-for-sale.

+ References

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- Definition

Fair value portion of notes payable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19,20,22)
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- Definition

The aggregate amount of the participation liability at the end of the accounting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377297&loc=d3e10013-112621

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