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Stockholders' Equity (DRSPP) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended | 172 Months Ended |
--- | --- | --- | --- | --- | ---
Dec. 31, 2020 | Sep. 30, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2017 | Aug. 08, 2013
Class of Stock [Line Items] |  |  |  |  |  |
Common stock, shares authorized (in shares) | 874,300,000 |  | 874,300,000 | 886,950,000 |  |
Issuance of stock, net of expenses (in shares) | 12,300,000 |  |  |  |  |
DRSPP |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Common stock, shares authorized (in shares) |  |  |  |  |  | 9,000,000.0
Shares of common stock authorized and available for issuance (in shares) | 8,700,000 |  | 8,700,000 |  |  |
Issuance of stock, net of expenses (in shares) |  | 379,903 | 235,635 | 322,888 | 34,614,403 |
Value of shares issued net of expenses |  | $ 2.8 | $ 1.0 | $ 2.4 | $ 287.6 |

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