CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED) (Parenthetical) (Dividend Declared March 4 2013 [Member], USD $)	3 Months Ended
Mar. 31, 2013
Dividend Declared March 4 2013 [Member]
Dividends Declared per Share of Common Stock, special dividend (in dollars per share)	$ 0.50

Represents the special dividend declared during the period for each share of common stock outstanding with cash dividends.

No definition available.

Name:	mfa_CommonStockSpecialDividendsPerShareDeclared
Namespace Prefix:	mfa_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration