Equity Compensation, Employment Agreements and Other Benefit Plans (Employment Agreements) (Details)	Dec. 31, 2017 officer
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of officers having employment agreements with the company	3

Represents the number of officers having employment agreements with the company.

No definition available.

Name:	mfa_EmploymentAgreementsNumberOfOfficers
Namespace Prefix:	mfa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant