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Equity (Stock Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2017 | Mar. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Equity [Abstract] |  |  |  |  |  |
Stock repurchased and retired during period, shares |  | 0.8 | 0.0 |  | 0.0 | 10.2
Common stock value acquired including acquisition costs |  | $ 8,300,000 |  |  |  | $ 98,400,000
Average cost per share | $ 11.51 | $ 10.22 |  |  |  | $ 9.67
Repurchase of common stock, authorized amount |  |  | $ 41,700,000.0 | $ 41,700,000.0 |  |
Class of Stock [Line Items] |  |  |  |  |  |
Shares repurchased (in shares) | 4.0 |  |  |  |  |
Repurchase of stock | $ 45,900,000 |  |  | $ 8,304,000 | $ 45,928,000 | $ 98,429,000
3.125% senior convertible notes |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Stated interest rate (percent) | 3.125% |  | 3.125% | 3.125% |  |

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