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Stockholders' Equity (Stock Repurchase Program) (Details) - USD ($) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Nov. 02, 2020 | Dec. 31, 2013
Share-based Payment Arrangement [Abstract] |  |  |  |  |
Stock repurchase program, authorized amount |  |  |  | $ 250,000,000 |
Number of shares authorized to be repurchased under the Repurchase Program (in shares) |  |  |  |  | 10,000,000
Number of remaining shares authorized to be repurchased under the Repurchase Program (in shares) |  |  |  |  | 6,600,000
Shares repurchased and retired (in shares) | 14,085,678 | 0 | 0 |  |
Average cost per share (usd per share) | $ 3.61 |  |  |  |
Cost for shares repurchased | $ 50,800,000 |  |  |  |
Payments for fees and commissions paid to the sales agent | $ 141,000 |  |  |  |
Warrants repurchased (in shares) | 17,593,576 |  |  |  |
Remaining authorized repurchase amount | $ 165,700,000 |  |  |  |

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