| Pay vs Performance Disclosure | 6 Months Ended | 12 Months Ended |
| Dec. 31, 2020 | Jun. 23, 2020 | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) |
| Pay vs Performance Disclosure [Table] | | | | | |
| Pay vs Performance [Table Text Block] | | | Value of Initial Fixed $100 (a) (b) Summary Compen-sation Table Total for Current CEO ($)(2) (b) (c) Compen-sation Actually Paid to Current CEO ($)(3) (c) Compen-sation Actually Paid to Prior CEO ($)(3) (d) Average Summary Compen-sation Table Total for Non-CEO NEOs ($)(4) (e) Average Compen-sation Actually Paid to Non-CEO NEOs ($)(3)(4) (f) Total Stockholder Return ($)(5) (g) Peer Group Total Stockholder Return ($)(5)(6) (k) Net Income ($)(7) (i) Company-Selected Measure: Relative Total Economic Return (8)(%ile) 2022 4,413,162 — 3,127,319 — 1,954,529 1,496,022 36.68 69.20 220,238,656 68.6% 2021 4,737,627 — 3,930,403 — 2,154,523 1,730,993 47.83 91.50 187,227,532 9.7% 2020 3,001,643 89,173 1,877,296 (551,392) 1,941,787 1,004,471 47.80 77.80 (1,630,135,126) 9.6% | | |
| Company Selected Measure Name | | | relative total economic return (rTER) | | |
| Named Executive Officers, Footnote [Text Block] | | | Mr. Greenberg was appointed as Chief Executive Officer in June 2020. We did not pay cash compensation to our former CEO, Thomas Siering, in 2020 and, accordingly, compensation information for Mr. Siering is limited to “Other Compensation” and equity awards. Individuals comprising the non-principal executive officers (non-PEOs) in columns (d) and (e) are: for 2022, Ms. Riskey, Mr. Letica, Ms. Sandberg, and Mr. Rush; for 2021, Ms. Riskey, Ms. Sandberg and Mr. Rush and, until his departure in June 2021, Matthew Koeppen; and for 2020, Ms. Riskey, Mr. Koeppen and Ms. Sandberg. As noted in the Summary Compensation Table, Mr. Letica was appointed as Chief Investment Officer in 2022, and Mr. Rush was not a named executive officer in 2020. | | |
| Peer Group Issuers, Footnote [Text Block] | | | As permitted by SEC rules, the Peer Group referenced for the purpose of the Peer Group Total Stockholder Return is the Bloomberg REIT Mortgage Index (BBRMTG). | | |
| Adjustment To PEO Compensation, Footnote [Text Block] | | | Reconciliation of Summary Compensation to Compensation Actually Paid The following reconciliation tables are included in order to illustrate the calculation of Compensation Actually Paid in the Pay Versus Performance table above on page 46 . Specifically, the following reconciliations show the amounts that were deducted from and added to the Summary Compensation Table total compensation shown on page 36 for the current CEO, the prior CEO, and the average of the other non-CEO named executive officers for each of the years reported. Year 2022 Reconciliation of Summary Compensation Table Totals to Compensation Actually Paid Current CEO Prior CEO Average for Non-CEO NEOs Summary Compensation Table Total $4,413,162 — $1,954,529 Deduction for amounts reported under the Stock Awards Column in the Summary Compensation Table $(2,051,674) — $(855,377) Increase for year-end fair value of any awards granted during the year that remain outstanding and unvested as of year-end $1,510,869 — $635,501 Increase (decrease) for change in value from prior year-end to current year-end of awards granted in prior years that were outstanding and unvested as of year-end $(683,237) — $(213,993) Increase (decrease) for change in fair value from prior year-end to vesting date of awards granted in prior years that vested during the year $(61,801) — $(24,638) Compensation Actually Paid $3,127,319 — $1,496,022 Year 2021 Reconciliation of Summary Compensation Table Totals to Compensation Actually Paid Current CEO Prior CEO Average for Non-CEO NEOs Summary Compensation Table Total $4,737,627 — $2,154,523 Deduction for amounts reported under the Stock Awards Column in the Summary Compensation Table $(2,727,749) — $(1,299,042) Increase for year-end fair value of any awards granted during the year that remain outstanding and unvested as of year-end $1,980,659 — $641,121 Increase (decrease) for change in value from prior year-end to current year-end of awards granted in prior years that were outstanding and unvested as of year-end $(43,562) — $(24,982) Increase for fair value on vesting date of any awards that were both granted and vested in the same year — — $250,567 Increase (decrease) for change in fair value from prior year-end to vesting date of awards granted in prior years that vested during the year $(16,572) — $8,806 Compensation Actually Paid $3,930,403 — $1,730,993 Year 2020 Reconciliation of Summary Compensation Table Totals to Compensation Actually Paid Current CEO Prior CEO Average for Non-CEO NEOs Summary Compensation Table Total $3,001,643 $89,173 $1,941,787 Deduction for amounts reported under the Stock Awards Column in the Summary Compensation Table $(1,499,987) — $(1,116,653) Increase for year-end fair value of any awards granted during the year that remain outstanding and unvested as of year-end $627,362 — $467,040 Increase (decrease) for change in value from prior year-end to current year-end of awards granted in prior years that were outstanding and unvested as of year-end $(274,643) $(714,780) $(306,919) Increase (decrease) for change in fair value from prior year-end to vesting date of awards granted in prior years that vested during the year $22,921 $74,215 $19,216 Compensation Actually Paid $1,877,296 $(551,392) $1,004,471 | | |
| Non-PEO NEO Average Total Compensation Amount | | | $ 1,954,529 | $ 2,154,523 | $ 1,941,787 |
| Non-PEO NEO Average Compensation Actually Paid Amount | | | $ 1,496,022 | 1,730,993 | 1,004,471 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | | | Reconciliation of Summary Compensation to Compensation Actually Paid The following reconciliation tables are included in order to illustrate the calculation of Compensation Actually Paid in the Pay Versus Performance table above on page 46 . Specifically, the following reconciliations show the amounts that were deducted from and added to the Summary Compensation Table total compensation shown on page 36 for the current CEO, the prior CEO, and the average of the other non-CEO named executive officers for each of the years reported. Year 2022 Reconciliation of Summary Compensation Table Totals to Compensation Actually Paid Current CEO Prior CEO Average for Non-CEO NEOs Summary Compensation Table Total $4,413,162 — $1,954,529 Deduction for amounts reported under the Stock Awards Column in the Summary Compensation Table $(2,051,674) — $(855,377) Increase for year-end fair value of any awards granted during the year that remain outstanding and unvested as of year-end $1,510,869 — $635,501 Increase (decrease) for change in value from prior year-end to current year-end of awards granted in prior years that were outstanding and unvested as of year-end $(683,237) — $(213,993) Increase (decrease) for change in fair value from prior year-end to vesting date of awards granted in prior years that vested during the year $(61,801) — $(24,638) Compensation Actually Paid $3,127,319 — $1,496,022 Year 2021 Reconciliation of Summary Compensation Table Totals to Compensation Actually Paid Current CEO Prior CEO Average for Non-CEO NEOs Summary Compensation Table Total $4,737,627 — $2,154,523 Deduction for amounts reported under the Stock Awards Column in the Summary Compensation Table $(2,727,749) — $(1,299,042) Increase for year-end fair value of any awards granted during the year that remain outstanding and unvested as of year-end $1,980,659 — $641,121 Increase (decrease) for change in value from prior year-end to current year-end of awards granted in prior years that were outstanding and unvested as of year-end $(43,562) — $(24,982) Increase for fair value on vesting date of any awards that were both granted and vested in the same year — — $250,567 Increase (decrease) for change in fair value from prior year-end to vesting date of awards granted in prior years that vested during the year $(16,572) — $8,806 Compensation Actually Paid $3,930,403 — $1,730,993 Year 2020 Reconciliation of Summary Compensation Table Totals to Compensation Actually Paid Current CEO Prior CEO Average for Non-CEO NEOs Summary Compensation Table Total $3,001,643 $89,173 $1,941,787 Deduction for amounts reported under the Stock Awards Column in the Summary Compensation Table $(1,499,987) — $(1,116,653) Increase for year-end fair value of any awards granted during the year that remain outstanding and unvested as of year-end $627,362 — $467,040 Increase (decrease) for change in value from prior year-end to current year-end of awards granted in prior years that were outstanding and unvested as of year-end $(274,643) $(714,780) $(306,919) Increase (decrease) for change in fair value from prior year-end to vesting date of awards granted in prior years that vested during the year $22,921 $74,215 $19,216 Compensation Actually Paid $1,877,296 $(551,392) $1,004,471 | | |
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | | | Relationship of Total Stockholder Return to Compensation Actually Paid The following graph illustrates the relationship between our total stockholder return (TSR) and the Compensation Actually Paid to our current CEO, our prior CEO and the average of other non-CEO named executive officers. As shown, Compensation Actually Paid generally aligns with TSR, primarily due to the company’s use of equity awards, which are tied directly to our stock price. For further information about our use of equity awards as a component of compensation is, please refer to “ Long-Term Incentive Compensation ” on page 29 . | | |
| Compensation Actually Paid vs. Net Income [Text Block] | | | Relationship of Net Income to Compensation Actually Paid The following graph illustrates the relationship between GAAP net income and the compensation actually paid to our current CEO, prior CEO and the average of other non-CEO named executive officers. The majority of our assets are carried at fair value, however, the unrealized gains and losses are included in either net income or accumulated other comprehensive income depending on the asset type. For this reason, net income is an incomplete measure and does not reflect the company’s total return. The Compensation Committee does not use net income as a performance measure in our executive compensation program. | | |
| Compensation Actually Paid vs. Company Selected Measure [Text Block] | | | Relationship of Relative Total Economic Return to Compensation Actually Paid The following graph illustrates the relationship between relative total economic return (rTER) and the Compensation Actually Paid to our current CEO, prior CEO and the average of other non-CEO named executive officers. We have designated rTER as our company selected measure in the Pay Versus Performance table. We believe this financial measure represents the most important financial performance measure we used in our annual incentive compensation plan to link Compensation Actually Paid to our named executive officers for the 2022 performance year. For information regarding our use of rTER in our annual incentive compensation program, please refer to “ Annual Incentive Compensation ” on page 26 . | | |
| Total Shareholder Return Vs Peer Group [Text Block] | | | The following graph compares our total stockholder return as compared to the Bloomberg REIT Mortgage Index for the years reported. | | |
| Tabular List [Table Text Block] | | | Most Important Performance Measures for 2022 Relative Total Economic Return Absolute Total Economic Return Relative 3-Year Total Stockholder Return Absolute 3-Year Total Stockholder Return Strategic and Operational Performance Goals and Objectives | | |
| Total Shareholder Return Amount | | | $ 36.68 | 47.83 | 47.80 |
| Peer Group Total Shareholder Return Amount | | | 69.20 | 91.50 | 77.80 |
| Net Income (Loss) | | | $ 220,238,656 | $ 187,227,532 | $ (1,630,135,126) |
| Company Selected Measure Amount | | | 0.686 | 0.097 | 0.096 |
| PEO Name | Mr. Greenberg | Thomas Siering | Mr. Greenberg | Mr. Greenberg | |
| Additional 402(v) Disclosure [Text Block] | | | As described in the “ Summary Compensation Table ” on page 36 and elsewhere in this proxy statement, prior to August 15, 2020, we were an externally managed company and did not pay any cash compensation to our named executive officers. Accordingly, cash compensation amounts for fiscal year 2020 reflect amounts paid to our NEOs beginning August 15, 2020. As required by Item 402(v) of Regulation S-K, reconciliation tables illustrating the calculation of Compensation Actually Paid are presented under “ Pay Versus Performance Supplemental Information — Reconciliation of Summary Compensation to Compensation Actually Paid ” below on page 47 . Represents GAAP Net Income as reported in our Annual Report on Form 10-K for the year ended December 31 for each of the years shown. See also “ Pay Versus Performance Supplemental Information — Relationship of Net Income to Compensation Actually Paid ” on page 49 below for further information. | | |
| Measure [Axis]: 1 | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Measure Name | | | Relative Total Economic Return | | |
| Non-GAAP Measure Description [Text Block] | | | We have designated relative total economic return (rTER) as our company selected measure for this table. We believe this additional financial measure represents the most important financial performance measure used by the company in its annual incentive compensation plan to link Compensation Actually Paid to our named executive officers for the 2022 performance year. As used in our annual incentive compensation plan, rTER compares our total economic return for the 12-month performance period ended September 30 to the total economic return of our performance group peers, however, in accordance with Regulation S-K, we have computed rTER for purposes of this table based on the year ended December 31 for each year reported. For further information on our annual cash incentive plan and how we use rTER as a performance metric in our compensation program, please refer to the section titled “ Annual Incentive Compensation ” above on page 26 . The companies included in our performance peer group for 2022 are included in the section titled “ Peer and Competitive Market Positioning" above on page 32 | | |
| Measure [Axis]: 2 | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Measure Name | | | Absolute Total Economic Return | | |
| Measure [Axis]: 3 | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Measure Name | | | Relative 3-Year Total Stockholder Return | | |
| Measure [Axis]: 4 | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Measure Name | | | Absolute 3-Year Total Stockholder Return | | |
| Measure [Axis]: 5 | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Measure Name | | | Strategic and Operational Performance Goals and Objectives | | |
| Greenberg [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| PEO Total Compensation Amount | | | $ 4,413,162 | $ 4,737,627 | $ 3,001,643 |
| PEO Actually Paid Compensation Amount | | | 3,127,319 | 3,930,403 | 1,877,296 |
| Siering [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| PEO Total Compensation Amount | | | | | 89,173 |
| PEO Actually Paid Compensation Amount | | | | | (551,392) |
| PEO [Member] | Greenberg [Member] | Stock Awards Adjustments [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | (2,051,674) | (2,727,749) | (1,499,987) |
| PEO [Member] | Greenberg [Member] | Equity Awards Granted During the Year, Unvested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | 1,510,869 | 1,980,659 | 627,362 |
| PEO [Member] | Greenberg [Member] | Equity Awards Granted in Prior Years, Unvested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | (683,237) | (43,562) | (274,643) |
| PEO [Member] | Greenberg [Member] | Equity Awards Granted in Prior Years, Vested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | (61,801) | (16,572) | 22,921 |
| PEO [Member] | Greenberg [Member] | Equity Awards Granted During the Year, Vested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | | 0 | |
| PEO [Member] | Siering [Member] | Stock Awards Adjustments [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | | | 0 |
| PEO [Member] | Siering [Member] | Equity Awards Granted During the Year, Unvested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | | | 0 |
| PEO [Member] | Siering [Member] | Equity Awards Granted in Prior Years, Unvested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | | | (714,780) |
| PEO [Member] | Siering [Member] | Equity Awards Granted in Prior Years, Vested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | | | 74,215 |
| Non-PEO NEO [Member] | Stock Awards Adjustments [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | (855,377) | (1,299,042) | (1,116,653) |
| Non-PEO NEO [Member] | Equity Awards Granted During the Year, Unvested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | 635,501 | 641,121 | 467,040 |
| Non-PEO NEO [Member] | Equity Awards Granted in Prior Years, Unvested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | (213,993) | (24,982) | (306,919) |
| Non-PEO NEO [Member] | Equity Awards Granted in Prior Years, Vested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | $ (24,638) | 8,806 | $ 19,216 |
| Non-PEO NEO [Member] | Equity Awards Granted During the Year, Vested [Member] | | | | | |
| Pay vs Performance Disclosure [Table] | | | | | |
| Adjustment to Compensation Amount | | | | $ 250,567 | |
