Fair Value of Financial Instruments - Schedule of the aggregate carrying value of debt and estimates of fair value (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured revolving credit facility	$ 285,000	$ 0
Term loan and credit facility	0	470,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured revolving credit facility	285,000	0
Term loan and credit facility	0	470,000
Mortgages \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	759,405	903,985
Mortgages \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	764,552	912,365
Convertible Debt \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	239,002	237,667
Convertible Debt \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	253,423	253,469
Senior Notes \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	350,000	0
Senior Notes \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable	$ 338,962	$ 0

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

Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Line-of-Credit Arrangement

-URI http://asc.fasb.org/extlink&oid=6517033

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- Definition

Fair value portion of contractual obligation to pay money on demand or on fixed or determinable dates.

+ References

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- Definition

Fair value portion of notes payable.

+ 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 210.5-02.19,20,22)

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

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