Significant Acquisitions and Dispositions (Narrative) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) buildings	Dec. 31, 2019 USD ($) buildings	Dec. 31, 2018 USD ($) buildings
Business Combinations [Abstract]
Payments to Acquire Commercial Real Estate	$ 383,672	$ 210,224	$ 348,107
Number of Real Estate Properties \| buildings	10	6	9
Real estate assets	$ 410,481	$ 205,390	$ 328,126
Lease related intangible assets	14,460	11,716	24,996
Total acquired assets	424,941	$ 217,106	353,122
Secured debt	25,455
Below market lease liabilities	$ 14,124		$ 505
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years 4 months 24 days	6 years 6 months	11 years 3 months 18 days

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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Amount of acquired leases acquired as part of a real property acquisition at below market lease rate with a finite life.

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Amount of assets acquired at the acquisition date.

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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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The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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

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The cash outflow from the acquisition of property as primarily intended to generate income for its owner.

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