Real Estate - Real Estate Under Development and Construction in Progress (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($) property	Dec. 31, 2015 USD ($) property
Property, Plant and Equipment [Line Items]
Real estate under development \| $	$ 543,486	$ 609,574
Real estate in service \| $	$ 2,551,448	$ 1,828,006
Core Portfolio [Member]
Property, Plant and Equipment [Line Items]
Number of real estate properties \| property	1
Fund II [Member]
Property, Plant and Equipment [Line Items]
Number of real estate properties \| property	2	2
Real estate in service \| $	$ 187,400
Fund II [Member] \| City Point [Member]
Property, Plant and Equipment [Line Items]
Real estate development, capitalized costs \| $	98,400
Fund II [Member] \| Other Properties [Member]
Property, Plant and Equipment [Line Items]
Real estate development, capitalized costs \| $	$ 22,900
Fund III [Member]
Property, Plant and Equipment [Line Items]
Number of real estate properties \| property	3	2
Fund IV [Member]
Property, Plant and Equipment [Line Items]
Number of real estate properties \| property	4	4
Number of properties acquired \| property	2

Number of Real Estate Properties Under Development

No definition available.

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- Definition

The current amount of expenditures for a real estate project that has not yet been completed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.10)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Phase
-URI http://asc.fasb.org/extlink&oid=49177889

+ Details

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- Definition

The number of businesses acquired by the entity during the period.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Carrying amount as of the balance sheet date of interest costs that were capitalized to properties under development during the land development and construction period of a project, and which are included in inventory.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

+ Details

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- Definition

Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

+ Details

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- Details

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