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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
	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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