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Forward Equity Sale Agreement (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 12 Months Ended |  | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2013 Equity Contract [Member] | Dec. 31, 2012 Amended and restated forward equity sale agreement [Member]
Forward equity sale agreement |  |  |
Value of common stock to sell under each agreement, maximum |  |  | $ 400.0
Notional amount sold | 77.0 |  | 147.2
Average share price (in dollars per share) | $ 185.56 |  | $ 121.37
Notional Amount |  | $ 70.2 |

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- Details
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- Definition Represents the maximum value of common stock under each forward equity sale agreements to sell shares of the entity's common stock. + References No definition available. + Details
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- Definition Represents the sum of common stock sold under the forward equity sale agreements. + References No definition available. + Details
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- Definition Represents the average share price of common stock sold under the forward equity sale agreements. + References No definition available. + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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