Represents the number of components that make up a linked transaction which is not reported separately but evaluated on a combined basis and reported as a forward (derivative) contract.

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- Definition

Represents the minimum percentage of annual taxable income which must be distributed to stockholders in order to comply with requirements of the federal tax law for treatment as a real estate investment trust.

+ Details

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- Definition

Represents the forfeiture rate applied to equity based awards granted in 2009 and prior years for determining the fair value of the awards.

+ Details

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- Definition

Represents the maximum 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.

+ Details

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Period Type:	duration

- Definition

Represents the minimum 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.

+ Details

Name:	mfa_ShareBasedCompensationArrangementByShareBasedPaymentAwardMarketConditionPeriodMinimum
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Data Type:	xbrli:integerItemType
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- Details

Name:	us-gaap_AccountingPoliciesAbstract
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- Definition

The maximum vesting term over 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.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

The minimum vesting term over 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.

+ Details

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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.

+ Details

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Summary of Significant Accounting Policies (Details 2)	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
Summary of Significant Accounting Policies (Details 2)	Sep. 30, 2011 M D Component Lease	Dec. 31, 2009	Sep. 30, 2011 Restricted Stock Units	Dec. 31, 2010 Restricted Stock Units Y
Summary of Significant Accounting Policies
Minimum annual taxable income distributable to stockholders (as a percent)	90.00%
Number of components in a linked transaction	2
Share based compensation
Forfeiture rate assumption for equity based awards granted in 2009 and prior years (as a percent)		0.00%
Vesting period of restricted share units ("RSUs"), minimum (in years)				2 year
Vesting period of restricted share units ("RSUs"), maximum (in years)			3 year	4 year
Minimum period for measuring market condition of award (in years)				2
Maximum period for measuring market condition of award (in years)				4