Summary of Investments in Real Estate (Parenthetical) (Detail) $ in Thousands	Jun. 30, 2018 USD ($) Property	Dec. 31, 2017 Property
Office and Retail
Real Estate Properties [Line Items]
Carrying value of asset held for sale \| $	$ 27,554
Office
Real Estate Properties [Line Items]
Number of real estate properties held for sale	1	0
Retail
Real Estate Properties [Line Items]
Number of real estate properties held for sale	1	0

Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Name:	us-gaap_RealEstateHeldforsale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant