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Stockholders' Equity (Public Offering) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Sep. 05, 2018 | Aug. 07, 2018 | Dec. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |
Shares issued (in shares) |  |  | 12,300 |  |  |
Payments made for costs related to common stock issuances |  |  |  | $ 0 | $ 0 | $ 329
Public Offering |  |  |  |  |  |
Subsidiary, Sale of Stock [Line Items] |  |  |  |  |  |
Shares Issued (in shares) |  | 50,875 |  |  |  |
Gross proceeds (usd per share) |  | $ 7.78 |  |  |  |
Gross Proceeds |  | $ 395,807 |  |  |  |
Shares issued (in shares) | 875 |  |  |  |  |
Payments made for costs related to common stock issuances | $ 6,400 |  |  |  |  |

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