Financing Arrangements, Portfolio Investments - Assets Pledged as Collateral (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	$ 1,287,314	$ 1,276,918
Fair Value of Collateral Pledged	1,470,903	1,453,699
Amortized Cost of Collateral Pledged	1,392,272	1,368,115
Consolidated K-Series
Financial Instruments Owned and Pledged as Collateral [Line Items]
K-Series, carrying value	484,800	468,000
Agency ARMs
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	80,977	86,349
Fair Value of Collateral Pledged	84,361	90,343
Amortized Cost of Collateral Pledged	87,132	92,586
Agency Fixed- Rate
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	853,390	842,474
Fair Value of Collateral Pledged	902,219	890,359
Amortized Cost of Collateral Pledged	933,829	902,744
Non-Agency RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	37,016	38,160
Fair Value of Collateral Pledged	49,205	51,841
Amortized Cost of Collateral Pledged	48,269	50,693
CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	315,931	309,935
Fair Value of Collateral Pledged	435,118	421,156
Amortized Cost of Collateral Pledged	323,042	322,092
CMBS \| Consolidated K-Series
Financial Instruments Owned and Pledged as Collateral [Line Items]
K-Series, carrying value	$ 393,400	$ 377,500

Amortized Cost Of Collateral Pledged.

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- Definition

Represents the aggregate carrying value of the investment in the multi-family loans held in securitization trusts.

+ References

No definition available.

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- Definition

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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- Definition

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(a)(i))
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(1))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 55
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-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
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- Definition

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
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