Organization - Additional Information (Detail)	Mar. 31, 2018 property
Operating Property
Real Estate Properties [Line Items]
Number of properties in greater New York City metropolitan area	7

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