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Summary of Significant Accounting Policies - Basis of Presentation and Real Estate Properties (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2017 building property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Basis of Presentation
Ownership interest in subsidiaries (as a percent)		100.00%
Number of properties included in joint venture agreement | property	1
Number of buildings included in joint venture agreement | building	2
Variable interest entity, consolidated, carrying amount of assets		$ 1,102,986
Variable interest entity, consolidated, carrying amount of liabilities		720,678
Increase in capitalized above and below market leases rental income		5,349	$ 4,941	$ 4,060
Amortization of acquired real estate leases and other intangible assets		$ 72,035	$ 92,818	$ 80,040
Land and Building | Real Estate Investment | Maximum
Basis of Presentation
Estimated useful lives		40 years

X

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) and liabilities in a systematic and rational manner to the periods expected to be impacted from such assets and liabilities. As a noncash expense/ income, this element is added back to/deducted from net income when calculating cash provided by (used in) operations using the indirect method.

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- Definition

Represents the increase or decrease in rental income associated with capitalized above market and below market lease due to amortization.

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- Definition

Number of Buildings Included in Joint Venture Agreement

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Number of Properties Included in Joint Venture Agreement

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- Definition

Represents the percentage of ownership held in the subsidiary either directly or indirectly.

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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5710-111685

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The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5710-111685

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