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Subsequent Events - Monthly Distributions Declared by Company's Board of Directors (Detail) - $ / shares | Jan. 05, 2021 | Dec. 31, 2020 | Dec. 24, 2020 | Dec. 23, 2020 | Dec. 04, 2020 | Nov. 30, 2020 | Nov. 25, 2020 | Nov. 20, 2020 | Nov. 05, 2020 | Oct. 30, 2020 | Oct. 27, 2020 | Oct. 23, 2020 | Oct. 13, 2020
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Subsequent Event | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.4374999
Subsequent Event | Series E Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  | 0.414063
Subsequent Event | Senior Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  | 0.2625
Subsequent Event | Series F Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  | 0.375
Subsequent Event | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.37545
Subsequent Event | October 2020 |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Record Date |  |  |  |  |  |  |  |  |  |  |  | Oct. 23, 2020 |
Payment Date |  |  |  |  |  |  |  |  |  | Oct. 30, 2020 |  |  |
Subsequent Event | October 2020 | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 0.1458333 |  |  |
Subsequent Event | October 2020 | Series E Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  | 0.138021 |  |  |
Subsequent Event | October 2020 | Senior Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Date |  |  |  |  |  |  |  |  | Nov. 05, 2020 |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  | $ 0.0875 |  |  |  |
Subsequent Event | October 2020 | Series F Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Record Date |  |  |  |  |  |  |  |  |  |  | Oct. 27, 2020 |  |
Payment Date |  |  |  |  |  |  |  |  | Nov. 05, 2020 |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  | $ 0.125 |  |  |  |
Subsequent Event | October 2020 | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 0.12515 |  |  |
Forecast | November 2020 |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Record Date |  |  |  |  |  |  |  | Nov. 20, 2020 |  |  |  |  |
Payment Date |  |  |  |  |  | Nov. 30, 2020 |  |  |  |  |  |  |
Forecast | November 2020 | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  | $ 0.1458333 |  |  |  |  |  |  |
Forecast | November 2020 | Series E Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  | 0.138021 |  |  |  |  |  |  |
Forecast | November 2020 | Senior Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Date |  |  |  |  | Dec. 04, 2020 |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  | $ 0.0875 |  |  |  |  |  |  |  |
Forecast | November 2020 | Series F Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Record Date |  |  |  |  |  |  | Nov. 25, 2020 |  |  |  |  |  |
Payment Date |  |  |  |  | Dec. 04, 2020 |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  | $ 0.125 |  |  |  |  |  |  |  |
Forecast | November 2020 | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  |  |  |  |  | $ 0.12515 |  |  |  |  |  |  |
Forecast | December 2020 |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Record Date |  |  |  | Dec. 23, 2020 |  |  |  |  |  |  |  |  |
Payment Date |  | Dec. 31, 2020 |  |  |  |  |  |  |  |  |  |  |
Forecast | December 2020 | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  | $ 0.1458333 |  |  |  |  |  |  |  |  |  |  |
Forecast | December 2020 | Series E Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  | 0.138021 |  |  |  |  |  |  |  |  |  |  |
Forecast | December 2020 | Senior Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Payment Date | Jan. 05, 2021 |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) | $ 0.0875 |  |  |  |  |  |  |  |  |  |  |  |
Forecast | December 2020 | Series F Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Record Date |  |  | Dec. 24, 2020 |  |  |  |  |  |  |  |  |  |
Payment Date | Jan. 05, 2021 |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) | $ 0.125 |  |  |  |  |  |  |  |  |  |  |  |
Forecast | December 2020 | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends Payable [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution per share (in dollars per share) |  | $ 0.12515 |  |  |  |  |  |  |  |  |  |  |

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