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Equity (Schedule of Stock Offering Program) (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
At The Market Stock Offering [Line Items] |  |  |
Stock Issued During Period, Shares, New Issues |  |  | 24,964,000
Proceeds, net of fees (in millions) | $ 211.4 | $ 244.4 | $ 848.2
At The Market Program |  |  |
At The Market Stock Offering [Line Items] |  |  |
Stock Issued During Period, Shares, New Issues | 8,459,430 | 8,422,498 | 8,883,014
Common Stock Issued Average Price Per Share | $ 23.60 | $ 27.75 | $ 26.85
Proceeds, net of fees (in millions) | $ 196.5 | $ 229.1 | $ 232.5

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