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Residential Whole Loans (Additional Credit Related Information) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | $ 569,835 |  |  |  |  |  |  |  | $ 569,835 |
2019 | 1,880,880 |  |  |  |  |  |  |  | 1,880,880 |
2018 | 833,693 |  |  |  |  |  |  |  | 833,693 |
2017 | 95,833 |  |  |  |  |  |  |  | 95,833 |
2016 | 11,960 |  |  |  |  |  |  |  | 11,960 |
Prior | 803,131 |  |  |  |  |  |  |  | 803,131 |
Total | 4,195,332 |  |  |  |  |  |  |  | 4,195,332 |
Gross write-offs, 2019 |  |  |  |  |  |  |  |  | 21 |
Gross write-offs, 2018 |  |  |  |  |  |  |  |  | 1,564 |
Gross write-offs, 2017 |  |  |  |  |  |  |  |  | 32 |
Gross write-offs, prior |  |  |  |  |  |  |  |  | 768 |
Year Ended December 31, 2020 Gross write-offs | 830 | $ 281 | $ 627 | $ 647 | $ 277 | $ 62 | $ 50 | $ 0 | 2,385 |
Net write-offs, 2019 |  |  |  |  |  |  |  |  | 21 |
Net write-offs, 2018 |  |  |  |  |  |  |  |  | 1,564 |
Net write-offs, 2017 |  |  |  |  |  |  |  |  | 32 |
Net write-offs, prior |  |  |  |  |  |  |  |  | 768 |
Total Recoveries |  |  |  |  |  |  |  |  | 0 |
Year Ended December 31, 2020 Net write-offs |  |  |  |  |  |  |  |  | 2,385 |
Purchased performing loans | 3,521,624 |  |  |  | 5,370,653 |  |  |  | 3,521,624 | $ 5,370,653
Debt-to-Value Ratio, Less than 80 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 507,736 |  |  |  |  |  |  |  | 507,736 |
2019 | 1,827,345 |  |  |  |  |  |  |  | 1,827,345 |
2018 | 808,770 |  |  |  |  |  |  |  | 808,770 |
2017 | 85,499 |  |  |  |  |  |  |  | 85,499 |
2016 | 10,469 |  |  |  |  |  |  |  | 10,469 |
Prior | 557,509 |  |  |  |  |  |  |  | 557,509 |
Total | 3,797,328 |  |  |  |  |  |  |  | 3,797,328 |
Debt-to-Value Ratio, 80 to 100 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 62,099 |  |  |  |  |  |  |  | 62,099 |
2019 | 53,535 |  |  |  |  |  |  |  | 53,535 |
2018 | 24,923 |  |  |  |  |  |  |  | 24,923 |
2017 | 10,334 |  |  |  |  |  |  |  | 10,334 |
2016 | 1,491 |  |  |  |  |  |  |  | 1,491 |
Prior | 245,622 |  |  |  |  |  |  |  | 245,622 |
Total | 398,004 |  |  |  |  |  |  |  | 398,004 |
Non-QM Loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 489,172 |  |  |  |  |  |  |  | 489,172 |
2019 | 1,140,719 |  |  |  |  |  |  |  | 1,140,719 |
2018 | 645,364 |  |  |  |  |  |  |  | 645,364 |
2017 | 76,181 |  |  |  |  |  |  |  | 76,181 |
2016 | 5,749 |  |  |  |  |  |  |  | 5,749 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 2,357,185 |  |  |  |  |  |  |  | 2,357,185 |
Gross write-offs, 2018 |  |  |  |  |  |  |  |  | 117 |
Year Ended December 31, 2020 Gross write-offs |  |  |  |  |  |  |  |  | 117 |
Net write-offs, 2018 |  |  |  |  |  |  |  |  | 117 |
Total Recoveries |  |  |  |  |  |  |  |  | 0 |
Year Ended December 31, 2020 Net write-offs |  |  |  |  |  |  |  |  | 117 |
Purchased performing loans | 2,357,185 |  |  |  | 3,707,245 |  |  |  | 2,357,185 | 3,707,245
Non-QM Loans | Debt-to-Value Ratio, Less than 80 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 429,241 |  |  |  |  |  |  |  | 429,241 |
2019 | 1,111,534 |  |  |  |  |  |  |  | 1,111,534 |
2018 | 621,201 |  |  |  |  |  |  |  | 621,201 |
2017 | 67,547 |  |  |  |  |  |  |  | 67,547 |
2016 | 5,597 |  |  |  |  |  |  |  | 5,597 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 2,235,120 |  |  |  |  |  |  |  | 2,235,120 |
Non-QM Loans | Debt-to-Value Ratio, 80 to 100 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 59,931 |  |  |  |  |  |  |  | 59,931 |
2019 | 29,185 |  |  |  |  |  |  |  | 29,185 |
2018 | 24,163 |  |  |  |  |  |  |  | 24,163 |
2017 | 8,634 |  |  |  |  |  |  |  | 8,634 |
2016 | 152 |  |  |  |  |  |  |  | 152 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 122,065 |  |  |  |  |  |  |  | 122,065 |
Rehabilitation loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 44,927 |  |  |  |  |  |  |  | 44,927 |
2019 | 460,377 |  |  |  |  |  |  |  | 460,377 |
2018 | 70,594 |  |  |  |  |  |  |  | 70,594 |
2017 | 5,903 |  |  |  |  |  |  |  | 5,903 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 581,801 |  |  |  |  |  |  |  | 581,801 |
Gross write-offs, 2019 |  |  |  |  |  |  |  |  | 21 |
Gross write-offs, 2018 |  |  |  |  |  |  |  |  | 1,447 |
Gross write-offs, 2017 |  |  |  |  |  |  |  |  | 32 |
Year Ended December 31, 2020 Gross write-offs |  |  |  |  |  |  |  |  | 1,500 |
Net write-offs, 2019 |  |  |  |  |  |  |  |  | 21 |
Net write-offs, 2018 |  |  |  |  |  |  |  |  | 1,447 |
Net write-offs, 2017 |  |  |  |  |  |  |  |  | 32 |
Total Recoveries |  |  |  |  |  |  |  |  | 0 |
Year Ended December 31, 2020 Net write-offs |  |  |  |  |  |  |  |  | 1,500 |
Purchased performing loans | 581,801 |  |  |  | 1,026,097 |  |  |  | 581,801 | 1,026,097
Rehabilitation loans | Debt-to-Value Ratio, Less than 80 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 44,153 |  |  |  |  |  |  |  | 44,153 |
2019 | 448,646 |  |  |  |  |  |  |  | 448,646 |
2018 | 70,046 |  |  |  |  |  |  |  | 70,046 |
2017 | 4,203 |  |  |  |  |  |  |  | 4,203 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 567,048 |  |  |  |  |  |  |  | 567,048 |
Rehabilitation loans | Debt-to-Value Ratio, 80 to 100 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 774 |  |  |  |  |  |  |  | 774 |
2019 | 11,731 |  |  |  |  |  |  |  | 11,731 |
2018 | 548 |  |  |  |  |  |  |  | 548 |
2017 | 1,700 |  |  |  |  |  |  |  | 1,700 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 14,753 |  |  |  |  |  |  |  | 14,753 |
Single-family rental loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 35,736 |  |  |  |  |  |  |  | 35,736 |
2019 | 279,784 |  |  |  |  |  |  |  | 279,784 |
2018 | 117,735 |  |  |  |  |  |  |  | 117,735 |
2017 | 13,119 |  |  |  |  |  |  |  | 13,119 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 446,374 |  |  |  |  |  |  |  | 446,374 |
Purchased performing loans | 446,374 |  |  |  | 460,742 |  |  |  | 446,374 | 460,742
Single-family rental loans | Debt-to-Value Ratio, Less than 80 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 34,342 |  |  |  |  |  |  |  | 34,342 |
2019 | 267,165 |  |  |  |  |  |  |  | 267,165 |
2018 | 117,523 |  |  |  |  |  |  |  | 117,523 |
2017 | 13,119 |  |  |  |  |  |  |  | 13,119 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 432,149 |  |  |  |  |  |  |  | 432,149 |
Single-family rental loans | Debt-to-Value Ratio, 80 to 100 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 1,394 |  |  |  |  |  |  |  | 1,394 |
2019 | 12,619 |  |  |  |  |  |  |  | 12,619 |
2018 | 212 |  |  |  |  |  |  |  | 212 |
2017 | 0 |  |  |  |  |  |  |  | 0 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 0 |  |  |  |  |  |  |  | 0 |
Total | 14,225 |  |  |  |  |  |  |  | 14,225 |
Seasoned performing loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 0 |  |  |  |  |  |  |  | 0 |
2019 | 0 |  |  |  |  |  |  |  | 0 |
2018 | 0 |  |  |  |  |  |  |  | 0 |
2017 | 0 |  |  |  |  |  |  |  | 0 |
2016 | 79 |  |  |  |  |  |  |  | 79 |
Prior | 136,185 |  |  |  |  |  |  |  | 136,185 |
Total | 136,264 |  |  |  |  |  |  |  | 136,264 |
Purchased performing loans | 136,264 |  |  |  | 176,569 |  |  |  | 136,264 | 176,569
Seasoned performing loans | Debt-to-Value Ratio, Less than 80 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 0 |  |  |  |  |  |  |  | 0 |
2019 | 0 |  |  |  |  |  |  |  | 0 |
2018 | 0 |  |  |  |  |  |  |  | 0 |
2017 | 0 |  |  |  |  |  |  |  | 0 |
2016 | 0 |  |  |  |  |  |  |  | 0 |
Prior | 130,316 |  |  |  |  |  |  |  | 130,316 |
Total | 130,316 |  |  |  |  |  |  |  | 130,316 |
Seasoned performing loans | Debt-to-Value Ratio, 80 to 100 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 0 |  |  |  |  |  |  |  | 0 |
2019 | 0 |  |  |  |  |  |  |  | 0 |
2018 | 0 |  |  |  |  |  |  |  | 0 |
2017 | 0 |  |  |  |  |  |  |  | 0 |
2016 | 79 |  |  |  |  |  |  |  | 79 |
Prior | 5,869 |  |  |  |  |  |  |  | 5,869 |
Total | 5,948 |  |  |  |  |  |  |  | 5,948 |
Purchased Credit Deteriorated Loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 0 |  |  |  |  |  |  |  | 0 |
2019 | 0 |  |  |  |  |  |  |  | 0 |
2018 | 0 |  |  |  |  |  |  |  | 0 |
2017 | 630 |  |  |  |  |  |  |  | 630 |
2016 | 6,132 |  |  |  |  |  |  |  | 6,132 |
Prior | 666,946 |  |  |  |  |  |  |  | 666,946 |
Total | 673,708 |  |  |  |  |  |  |  | 673,708 |
Gross write-offs, prior |  |  |  |  |  |  |  |  | 768 |
Year Ended December 31, 2020 Gross write-offs |  |  |  |  |  |  |  |  | 768 |
Net write-offs, prior |  |  |  |  |  |  |  |  | 768 |
Total Recoveries |  |  |  |  |  |  |  |  | 0 |
Year Ended December 31, 2020 Net write-offs |  |  |  |  |  |  |  |  | 768 |
Purchased Credit Deteriorated Loans | Debt-to-Value Ratio, Less than 80 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 0 |  |  |  |  |  |  |  | 0 |
2019 | 0 |  |  |  |  |  |  |  | 0 |
2018 | 0 |  |  |  |  |  |  |  | 0 |
2017 | 630 |  |  |  |  |  |  |  | 630 |
2016 | 4,872 |  |  |  |  |  |  |  | 4,872 |
Prior | 427,193 |  |  |  |  |  |  |  | 427,193 |
Total | 432,695 |  |  |  |  |  |  |  | 432,695 |
Purchased Credit Deteriorated Loans | Debt-to-Value Ratio, 80 to 100 Percent |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
2020 | 0 |  |  |  |  |  |  |  | 0 |
2019 | 0 |  |  |  |  |  |  |  | 0 |
2018 | 0 |  |  |  |  |  |  |  | 0 |
2017 | 0 |  |  |  |  |  |  |  | 0 |
2016 | 1,260 |  |  |  |  |  |  |  | 1,260 |
Prior | 239,753 |  |  |  |  |  |  |  | 239,753 |
Total | 241,013 |  |  |  |  |  |  |  | 241,013 |
Settled Whole Loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
Total | 4,108,499 |  |  |  | 6,066,345 |  |  |  | 4,108,499 | 6,066,345
Settled Whole Loans | Non-QM Loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
Purchased performing loans | 2,336,117 |  |  |  | 3,706,857 |  |  |  | $ 2,336,117 | $ 3,706,857
Weighted average LTV ratio |  |  |  |  |  |  |  |  | 64.00% | 67.00%
Settled Whole Loans | Rehabilitation loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
Purchased performing loans | 563,430 |  |  |  | 1,023,766 |  |  |  | $ 563,430 | $ 1,023,766
Weighted average LTV ratio |  |  |  |  |  |  |  |  | 63.00% | 64.00%
Settled Whole Loans | Single-family rental loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
Purchased performing loans | 442,456 |  |  |  | 460,679 |  |  |  | $ 442,456 | $ 460,679
Weighted average LTV ratio |  |  |  |  |  |  |  |  | 70.00% | 70.00%
Settled Whole Loans | Seasoned performing loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
Purchased performing loans | 136,157 |  |  |  | 176,569 |  |  |  | $ 136,157 | $ 176,569
Weighted average LTV ratio |  |  |  |  |  |  |  |  | 40.00% | 46.00%
Settled Whole Loans | Certain rehabilitation loans |  |  |  |  |  |  |  |  |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |  |  |  |  |  |  |  |  |
Purchased performing loans | $ 189,900 |  |  |  | $ 269,200 |  |  |  | $ 189,900 | $ 269,200
Weighted average LTV ratio |  |  |  |  |  |  |  |  | 68.00% | 69.00%

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- Definition Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Gross Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated Five or More Years before Latest Fiscal Year, Net Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated In Fiscal Year Before Fiscal Year, Gross Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated In Fiscal Year before Latest Fiscal Year, Net Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated Three Years before Latest Fiscal Year, Gross Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated Three Years before Latest Fiscal Year, Net Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated Two Years before Latest Fiscal Year, Gross Write-Offs + References No definition available. + Details
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- Definition Financing Receivable, Originated Two Years before Latest Fiscal Year, Net Write-Offs + References No definition available. + Details
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- Definition Purchased Performing Loans + References No definition available. + Details
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Balance Type: | debit
Period Type: | instant

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- Definition 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 + References No definition available. + Details
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Namespace Prefix: | mfa_
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- Definition Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 + Details
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- Definition Amount of increase in allowance for credit loss on financing receivable from recovery. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 + Details
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