Acquisitions - Purchase Price Allocation for Acquisitions (Parenthetical) - (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired In-Place Leases
Business Acquisition [Line Items]
Weighted average amortization period	15 years	17 years	18 years
Acquired Above-Market Leases
Business Acquisition [Line Items]
Weighted average amortization period	17 years	17 years	18 years
Acquired Below-Market Leases
Business Acquisition [Line Items]
Weighted average amortization period	19 years	17 years	18 years

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