Real Estate (Dispositions) (Details) - Assets Held-for-sale $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($) property	Sep. 30, 2016 USD ($) property	Sep. 30, 2017 USD ($) property	Sep. 30, 2016 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of sold properties - gain on disposition of real estate \| property	6	7	31	24
Gain on disposition of real estate \| $	$ 3,185	$ 4,505	$ 20,864	$ 22,558

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2941-110230

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Balance Type:	credit
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