Real Estate Investments (Details Textual) $ in Thousands, ft² in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) ft²	Jun. 30, 2018 USD ($) ft²	Dec. 31, 2017 USD ($) ft²
Real Estate Properties [Line Items]
Number of Real Estate Properties	481	481	436
Land Subject to Ground Leases \| ft²	9.3	9.3	8.7
Real Estate Investment Property, Net, Total	$ 1,324,218	$ 1,324,218	$ 1,214,016
Impairment of Long-Lived Assets Held-for-use	1,200	1,200
Options Exercised [Member]
Real Estate Properties [Line Items]
Proceeds from Sale of Real Estate		3,900
Gains (Losses) on Sales of Investment Real Estate		1,000
Five Development And PCS Projects [Member]
Real Estate Properties [Line Items]
Property Subject to or Available for Operating Lease, Gross	16,800	16,800
Nine Development And PCS Projects [Member]
Real Estate Properties [Line Items]
Property Subject to or Available for Operating Lease, Gross	51,600	51,600
Five Real Estate Properties [Member]
Real Estate Properties [Line Items]
Proceeds from Sale of Real Estate		26,700
Gains (Losses) on Sales of Investment Real Estate	2,400	6,000
Seventy Nine Retail Net Lease Assets [Member]
Real Estate Properties [Line Items]
Payments to Acquire Property, Plant, and Equipment	$ 101,000	$ 199,800
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (in year)	12 years 4 months 24 days	13 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Land	$ 47,200	$ 47,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings	98,300	98,300
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	$ 54,300	$ 54,300

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Name Accounting Standards Codification
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Amount of facility held for productive use including, but not limited to, office, production, storage and distribution facilities, acquired at the acquisition date.

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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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Amount of real estate acquired, at the acquisition date.

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The net gain (loss) resulting from sales and other disposals of real estate owned for investment purposes.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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Area of land subject to a ground lease.

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The number of real estate properties owned as of the balance sheet date.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Cash received for the sale of real estate that is not part of an investing activity during the current period.

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Amount before accumulated depreciation of physical assets used in the normal conduct of business to produce goods and services subject to or available for lease.

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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.

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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.

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