Financing Arrangements, Portfolio Investments - Assets Pledged as Collateral (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	$ 608,304	$ 773,142
Fair Value of Collateral Pledged	731,855	945,143
Amortized Cost of Collateral Pledged	689,722	889,327
Consolidated K-Series
Financial Instruments Owned and Pledged as Collateral [Line Items]
K-Series, carrying value	408,700	314,900
Agency ARMs
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	80,327	102,088
Fair Value of Collateral Pledged	85,117	109,552
Amortized Cost of Collateral Pledged	85,990	110,903
Agency Fixed Rate
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	248,936	289,619
Fair Value of Collateral Pledged	261,450	308,411
Amortized Cost of Collateral Pledged	270,587	318,544
Agency IOs/U.S. Treasury Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	26,048	60,862
Fair Value of Collateral Pledged	36,702	82,153
Amortized Cost of Collateral Pledged	47,913	93,819
Non Agency
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	48,773	113,749
Fair Value of Collateral Pledged	64,917	150,944
Amortized Cost of Collateral Pledged	63,792	149,969
CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Outstanding Financing Arrangements	204,220	206,824
Fair Value of Collateral Pledged	283,669	294,083
Amortized Cost of Collateral Pledged	221,440	216,092
CMBS \| Consolidated K-Series
Financial Instruments Owned and Pledged as Collateral [Line Items]
K-Series, carrying value	$ 237,800	$ 254,600

Amortized Cost Of Collateral Pledged.

No definition available.

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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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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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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-SubTopic 20
-Section 55
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=49176635&loc=d3e9760-107771

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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)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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