Real Estate (Dispositions) (Details) - Assets Held-for-sale $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) property	Sep. 30, 2017 USD ($) property	Sep. 30, 2018 USD ($) property	Sep. 30, 2017 USD ($) 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	18	6	46	31
Gain on disposition of real estate \| $	$ 14,348	$ 3,185	$ 57,050	$ 20,864

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/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration