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Earnings Per Share - Antidilutive Securities (Details) | 3 Months Ended | 9 Months Ended
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Sep. 30, 2019 shares | Sep. 30, 2018 shares | Sep. 30, 2019 trading_day
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |
Series J convertible perpetual preferred stock | shares | 16,306 | 15,703 |
3.125% senior convertible notes |  |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |
Stated interest rates (as a percent) | 3.125% |  | 3.125%
Threshold consecutive trading days | trading_day |  |  | 40

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