Investments in Real Estate - Weighted Average Lives (Details)	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Investments [Abstract]
Acquired intangible assets (in years)	8 years 4 months 12 days	11 years 3 months 18 days
Acquired intangible liabilities (in years)	8 years 4 months 12 days	10 years 2 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration