Repurchase Agreements - Summary of Repurchase Agreements (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Collateral Assets	$ 3,369,887	$ 2,165,664
Outstanding Balance	$ 2,646,334	$ 1,713,723
Barclays MRA [Member]
Debt Instrument [Line Items]
Weighted Average Maturity Date	Sep. 29, 2021	Sep. 29, 2021
Security Interests	CMBS	CMBS
Collateral Assets	$ 988,935	$ 989,059
Outstanding Balance	$ 750,000	$ 750,000
Prepayment Provisions	None	None
RBC MRA [Member]
Debt Instrument [Line Items]
Weighted Average Maturity Date	Dec. 02, 2019	Jun. 18, 2019
Security Interests	CMBS	CMBS
Collateral Assets	$ 1,417,654	$ 794,917
Outstanding Balance	$ 1,132,662	$ 650,018
Prepayment Provisions	None	None
MS MRA [Member]
Debt Instrument [Line Items]
Weighted Average Maturity Date	Oct. 15, 2019	Jan. 15, 2019
Security Interests	CMBS/RMBS	CMBS
Collateral Assets	$ 531,410	$ 173,050
Outstanding Balance	$ 442,241	$ 146,569
Prepayment Provisions	None	None
Citi MRA [Member]
Debt Instrument [Line Items]
Weighted Average Maturity Date	Oct. 19, 2019	Jan. 13, 2019
Security Interests	CMBS	CMBS
Collateral Assets	$ 343,158	$ 193,372
Outstanding Balance	$ 254,324	$ 154,736
Prepayment Provisions	None	None
MUFG MRA [Member]
Debt Instrument [Line Items]
Weighted Average Maturity Date	Apr. 30, 2020	Apr. 30, 2020
Security Interests	CMBS	CMBS
Collateral Assets	$ 83,975	$ 15,266
Outstanding Balance	$ 63,532	$ 12,400
Prepayment Provisions	None	None
BAML MRA [Member]
Debt Instrument [Line Items]
Weighted Average Maturity Date	Oct. 23, 2019
Security Interests	CMBS
Collateral Assets	$ 4,755
Outstanding Balance	$ 3,575
Prepayment Provisions	None

Debt instrument prepayment provisions.

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- Definition

Repurchase agreements, security interests.

+ References

No definition available.

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Weighted average maturity date.

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- Definition

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- Definition

The fair value, as of the date of each statement of financial position presented, of securities which are owned but transferred to serve as collateral for the payment of repurchase agreements, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

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- Definition

Carrying value, as of the balance sheet date, of securities sold under agreements to repurchase where the transferor maintains effective control over the assets, accounting for them as secured debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 10
-Section 55
-Paragraph 51
-URI http://asc.fasb.org/extlink&oid=116647374&loc=d3e101761-111710

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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