EPS Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic Earnings/(Loss) per Share:
Net income/(loss) to common stockholders	$ 96,578	$ (908,995)	$ 93,040	$ 88,857	$ (812,417)	$ 181,897
Dividends declared on preferred stock	(8,144)		(3,750)	$ (3,750)	(13,359)	(7,500)
Dividends, dividend equivalents and undistributed earnings allocated to participating securities	(297)		(276)		0	(532)
Net income/(loss) to common stockholders - basic	$ 88,137		$ 89,014		$ (825,776)	$ 173,865
Basic weighted average common shares outstanding (in shares)	453,205		450,538		453,092	450,449
Basic (Loss)/Earnings per Share (usd per share)	$ 0.19		$ 0.20		$ (1.82)	$ 0.39
Diluted Earnings/(Loss) per Share:
Net income/(loss) to common stockholders - basic	$ 88,137		$ 89,014		$ (825,776)	$ 173,865
Interest expense on Convertible Senior Notes	3,893		1,206		0	1,206
Net income/(loss) to common stockholders - diluted	$ 92,030		$ 90,220		$ (825,776)	$ 175,071
Basic weighted average common shares outstanding (in shares)	453,205		450,538		453,092	450,449
Effect of assumed Convertible Senior Notes conversion to common shares (in shares)	28,920		8,898		0	4,474
Effect of Warrants (in shares)	375		0		0	0
Diluted weighted average common shares outstanding (in shares)	482,500		459,436		453,092	454,923
Diluted EPS (usd per share)	$ 0.19		$ 0.20		$ (1.82)	$ 0.38
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)					38,600
RSUs
Diluted Earnings/(Loss) per Share:
Weighted average grant date fair value (in dollars per share)	7.63				$ 7.63
Warrant
Diluted Earnings/(Loss) per Share:
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)					37,000
Weighted average grant date fair value (in dollars per share)	$ 1.87				$ 1.87

Participating Securities, Distributed and Undistributed Earnings (Loss), Basic and Diluted

No definition available.

Name:	mfa_ParticipatingSecuritiesDistributedandUndistributedEarningsLossBasicandDiluted
Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.