Summary of Significant Accounting Policies - Residential Whole Loans (Details)	3 Months Ended
Mar. 31, 2017
Accounting Policies [Abstract]
Number of days considered to classify loans delinquent	60 days
LTV ratio percentage (or less than)	80.00%

The LTV of which the Company has assessed its residential whole loans at carrying value will have a higher likelihood of default than newly originated mortgage loans

No definition available.

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