Organization and Business - Additional Information (Details) ft² in Millions	9 Months Ended
Sep. 30, 2018 ft² Properties
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of office properties \| Properties	12
Area of office and retail properties \| ft²	11.9
Percentage of ownership in operating partnership	90.50%

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration