Impairments (Details) $ 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
Asset Impairment Charges [Abstract]
Total provisions for impairment \| $	$ 6,900	$ 365	$ 25,000	$ 8,100
Number of impaired properties held-for-sale	12		16
Number of impaired properties held-for-investment			2	4
Number of impaired properties sold	7	4	21	17

The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2611-110228

Name:	us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration