Real Estate (Carrying Value of Properties) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Real Estate Investment Property, at Cost [Abstract]
Land and Land Improvements	$ 1,256,706	$ 1,023,553
Building and improvements	4,655,784	4,113,163
Total Real Estate	5,912,490	5,136,716
Accumulated Depreciation	974,972	851,624
Depreciation	143,400	148,900	$ 166,800
Industrial Property
Real Estate Investment Property, at Cost [Abstract]
Land and Land Improvements	1,233,655	1,000,810
Building and improvements	4,353,225	3,867,834
Total Real Estate	5,586,880	4,868,644
Accumulated Depreciation	926,703	810,044
Office properties
Real Estate Investment Property, at Cost [Abstract]
Land and Land Improvements	23,051	22,743
Building and improvements	302,559	245,329
Total Real Estate	325,610	268,072
Accumulated Depreciation	$ 48,269	$ 41,580

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
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Aggregate of the carrying amounts as of the balance sheet date of investments in building and building improvements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
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Amount before accumulated deprecation and depletion of real estate held for productive use and additions or improvements to real estate held for productive use, examples include, but are not limited to, walkways, driveways, fences, and parking lots. Excludes land held for sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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The cumulative amount of depreciation for real estate property held for investment purposes.

+ References

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-Name Accounting Standards Codification
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Amount of real estate investment property 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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