Represents the period over which changes in the entity's closing stock price and dividends declared on the entity's common stock are measured to determine stockholder returns that represent a market condition upon which an employee's right to exercise an award is contingent.

No definition available.

+ Details

Name:	mfa_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionPeriod
Namespace Prefix:	mfa_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement by Share Based Payment Award, Forfeiture Rate, Prior Years

+ References

No definition available.

+ Details

Name:	mfa_ShareBasedCompensationArrangementbyShareBasedPaymentAwardForfeitureRatePriorYears
Namespace Prefix:	mfa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Summary of Significant Accounting Policies-Equity Based Compensation (Details)	9 Months Ended	12 Months Ended	21 Months Ended	36 Months Ended
	Sep. 30, 2015	Dec. 31, 2010	Sep. 30, 2015	Dec. 31, 2013
Share based compensation
Forfeiture rate assumption for equity based awards granted in 2009 and prior years (as a percent)	0.00%
Restricted Stock Units
Share based compensation
Vesting period of restricted share units (RSUs)			3 years
Period for measuring market condition of award			3 years	3 years
Restricted Stock Units \| Minimum
Share based compensation
Vesting period of restricted share units (RSUs)		2 years		1 year
Period for measuring market condition of award		2 years
Restricted Stock Units \| Maximum
Share based compensation
Vesting period of restricted share units (RSUs)		4 years		3 years
Period for measuring market condition of award		4 years