Real Estate - Investments in Real Estate Properties (Parenthetical) (Detail) - a	Dec. 31, 2017	Dec. 31, 2016
Land [Member]
Real Estate Properties [Line Items]
Square feet	5,191	5,892

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_RealEstatePropertiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration