Debt - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Unsecured Debt [Member]
Debt Instrument [Line Items]
Unamortized premium	$ 17.3	$ 27.5
Unamortized debt issuance expense	16.4	13.9
Unsecured Line of Credit [Member]
Debt Instrument [Line Items]
Unamortized debt issuance expense	3.6	3.6
Mortgage Notes [Member]
Debt Instrument [Line Items]
Unamortized premium	69.3	83.8
Unamortized debt issuance expense	$ 10.7	$ 11.9

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

The amount of debt premium that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Details

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