Investments in Real Estate-Related Securities and Loans - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Marketable Securities [Line Items]
Investments in securities, cost basis	$ 3,760,776		$ 3,760,776		$ 2,281,416
Net unrealized gain (loss) on investments in Real Estate Related Securities and Loans	13,200	$ 4,900	65,000	$ 8,800
Realized gain on sale of CMBS positions	400		300
Commercial Mortgage Backed Securities Collateralized by Pools of Commercial Real Estate Debt [Member]
Marketable Securities [Line Items]
Investments in securities, cost basis	100,500	$ 0	100,500	$ 0
Interest income recorded	$ 1,700		$ 5,000

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(b))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

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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.

+ References

No definition available.

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Amortized cost of investments in debt securities classified as trading.

+ References

No definition available.

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