Collateral Positions (Details 2) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	$ 11,608,706
Legacy Non-Agency MBS
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	3,151,386
Agency Mortgage Backed Securities
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	4,979,926
RPL/NPL MBS
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	2,592,693
U.S. Treasury securities
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	498,336
CRT securities
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	116,770
Residential whole loans
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	201,538
Cash
Collateral Positions
Total Fair Value of Assets Pledged and Accrued Interest	68,057
Securities Sold under Agreements to Repurchase
Collateral Positions
Fair Value	11,471,855
Amortized Cost	10,793,526
Accrued Interest on Pledged Assets	24,805
Securities Sold under Agreements to Repurchase \| Legacy Non-Agency MBS
Collateral Positions
Fair Value	3,139,828
Amortized Cost	2,530,267
Accrued Interest on Pledged Assets	11,558
Non-Agency MBS acquired from consolidated VIEs in connection with resecuritization transactions	587,100	$ 1,275,000
Non-Agency MBS pledged as collateral in connection with contemporaneous repurchase and reverse repurchase agreements entered into with a single counterparty	723,600	$ 731,000
Securities Sold under Agreements to Repurchase \| Agency Mortgage Backed Securities
Collateral Positions
Fair Value	4,923,712
Amortized Cost	4,862,558
Accrued Interest on Pledged Assets	11,501
Securities Sold under Agreements to Repurchase \| RPL/NPL MBS
Collateral Positions
Fair Value	2,591,503
Amortized Cost	2,590,170
Accrued Interest on Pledged Assets	1,190
Securities Sold under Agreements to Repurchase \| U.S. Treasury securities
Collateral Positions
Fair Value	498,336
Amortized Cost	498,336
Accrued Interest on Pledged Assets	0
Securities Sold under Agreements to Repurchase \| CRT securities
Collateral Positions
Fair Value	116,690
Amortized Cost	115,276
Accrued Interest on Pledged Assets	80
Securities Sold under Agreements to Repurchase \| Residential whole loans
Collateral Positions
Fair Value	201,062
Amortized Cost	196,195
Accrued Interest on Pledged Assets	476
Securities Sold under Agreements to Repurchase \| Cash
Collateral Positions
Fair Value	724
Amortized Cost	724
Accrued Interest on Pledged Assets	0
Derivative Hedging Instruments
Collateral Positions
Fair Value	111,954
Amortized Cost	112,842
Accrued Interest on Pledged Assets	92
Derivative Hedging Instruments \| Legacy Non-Agency MBS
Collateral Positions
Fair Value	0
Amortized Cost	0
Accrued Interest on Pledged Assets	0
Derivative Hedging Instruments \| Agency Mortgage Backed Securities
Collateral Positions
Fair Value	44,621
Amortized Cost	45,509
Accrued Interest on Pledged Assets	92
Derivative Hedging Instruments \| RPL/NPL MBS
Collateral Positions
Fair Value	0
Amortized Cost	0
Accrued Interest on Pledged Assets	0
Derivative Hedging Instruments \| U.S. Treasury securities
Collateral Positions
Fair Value	0
Amortized Cost	0
Accrued Interest on Pledged Assets	0
Derivative Hedging Instruments \| CRT securities
Collateral Positions
Fair Value	0
Amortized Cost	0
Accrued Interest on Pledged Assets	0
Derivative Hedging Instruments \| Residential whole loans
Collateral Positions
Fair Value	0
Amortized Cost	0
Accrued Interest on Pledged Assets	0
Derivative Hedging Instruments \| Cash
Collateral Positions
Fair Value	67,333
Amortized Cost	67,333
Accrued Interest on Pledged Assets	$ 0

Represents the amount of interest receivable on securities pledged as collateral.

No definition available.

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Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

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- Definition

For an unclassified balance sheet, represents investments in debt and equity securities, categorized neither as held-to-maturity nor trading, which are acquired from a consolidated variable interest entity and eliminated on the entity's consolidated balance sheet.

+ References

No definition available.

+ Details

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Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the non-agency MBS pledged as collateral in connection with contemporaneous repurchase and reverse repurchase agreements entered into with a single counterparty.

+ References

No definition available.

+ Details

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- Definition

Sum of the fair values as of the date of the latest financial statement presented of securities pledged as collateral and the amount of interest receivable on the securities pledged as collateral.

+ References

No definition available.

+ Details

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Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
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- Definition

Represents the cost of debt and equity securities pledged as collateral, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

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Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ 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=55761124&loc=SL6224234-111729

+ Details

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- Details

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