Fair Value of Financial Instruments - Carrying Value and Estimated Fair Value of Company's Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participations sold	$ (50,709)	$ (34,974)
Debt related to real estate owned, held for sale	(33,000)	(33,000)
Commercial Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participations sold	(23,974)	(9,217)
Subordinate Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Participations sold	(26,735)	(25,757)
Carrying Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash and cash equivalents	294,060	325,498
Carrying Value \| Level III
Accounts, Notes, Loans and Financing Receivable [Line Items]
Secured debt arrangements, net	(3,418,579)	(3,436,672)
Senior secured term loan, net	(775,974)	(483,465)
Participations sold	(50,709)	(34,974)
Debt related to real estate owned, held for sale	(33,000)	(33,000)
Carrying Value \| Level III \| 2022 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(341,035)	(340,361)
Carrying Value \| Level III \| 2023 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(225,676)	(225,293)
Carrying Value \| Level III \| Commercial Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,754,258	5,451,084
Carrying Value \| Level III \| Subordinate Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,065,816	1,045,893
Estimate of Fair Value Measurement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash and cash equivalents	294,060	325,498
Estimate of Fair Value Measurement \| Level III
Accounts, Notes, Loans and Financing Receivable [Line Items]
Secured debt arrangements, net	(3,418,579)	(3,436,672)
Senior secured term loan, net	(781,767)	(475,263)
Participations sold	(50,646)	(34,919)
Debt related to real estate owned, held for sale	(33,000)	(33,000)
Estimate of Fair Value Measurement \| Level III \| 2022 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(342,764)	(327,381)
Estimate of Fair Value Measurement \| Level III \| 2023 Notes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes	(226,870)	(214,875)
Estimate of Fair Value Measurement \| Level III \| Commercial Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,679,416	5,361,948
Estimate of Fair Value Measurement \| Level III \| Subordinate Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,058,560	$ 1,027,582

Debt Related To Real Estate Owned, Held For Sale

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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.

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

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

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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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