Significant Acquisitions and Dispositions (Summary of Allocation of Fair Value of Amounts Recognized) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) buildings	Dec. 31, 2018 USD ($) buildings	Dec. 31, 2017 USD ($) buildings
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 217,106	$ 353,122	$ 992,651
Payments to Acquire Real Estate	$ 210,224	$ 348,107	$ 982,598
Number of Real Estate Properties \| buildings	6	9	28
Business Combination, Consideration Transferred		$ 505	$ 1,483
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		352,617	$ 991,168
Investments in and advances to unconsolidated companies	$ (133,074)	$ (110,795)
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years 6 months	11 years 3 months 18 days	8 years 8 months 12 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 assets acquired at the acquisition date.

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Amount of other liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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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 a piece of land, anything permanently fixed to it, including buildings, structures on it and so forth; includes real estate intended to generate income for the owner; excludes real estate acquired for use by the owner.

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The carrying amount of investments in unconsolidated real estate and other joint ventures not separately presented. This includes direct and indirect investments.

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