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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
At The Market Stock Offering [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues | [1] | 24,964,000 |  |
Proceeds, net of fees (in millions) |  | $ 848.2 | $ 336.7 | $ 23.1
At The Market Program |  |  |  |
At The Market Stock Offering [Line Items] |  |  |  |
Stock Issued During Period, Shares, New Issues |  | 8,883,014 | 11,931,376 | 0
Common Stock Issued Average Price Per Share |  | $ 26.85 | $ 26.58 | $ 0.00
Proceeds, net of fees (in millions) |  | $ 232.5 | $ 314.7 | $ 0.0
[1] | See Note 12, "Equity," for additional information.

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