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Forward Equity and Equity Distribution Program (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Jun. 30, 2016 | Sep. 30, 2016 | Sep. 30, 2016 | Sep. 30, 2015
Class of Stock [Line Items] |  |  |  |
Proceeds from issuance of common stock |  |  | $ 163.2 | $ 54.0
Forward Equity Agreement |  |  |  |
Class of Stock [Line Items] |  |  |  |
Number of shares available for sale under agreement (in shares) | 2.9 |  |  |
Common stock price (in dollars per share) | $ 167.25 |  |  |
Number of common shares issued (in shares) |  | 0.9 | 0.9 |
Proceeds from issuance of common stock |  | $ 150.3 |  |
Number of common stock shares unsettled (in shares) |  | 2.0 | 2.0 |
Stock repurchase program, authorized amount |  | $ 500.0 | $ 500.0 |

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