Mortgages Payable and Debt Maturities - Summary of Mortgage Payable (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Mortgages payable	$ 34,352	$ 34,851
4.98% Mortgage Note Due January 1, 2021 [Member]
Debt Instrument [Line Items]
Mortgages payable	2,763	2,807
4.065% Mortgage Note Due April 1, 2023 [Member]
Debt Instrument [Line Items]
Mortgages payable	3,858	3,932
5.26% Mortgage Note Due November 1, 2023 [Member]
Debt Instrument [Line Items]
Mortgages payable	3,747	3,800
4.4625% Mortgage Note Due December 6, 2024 [Member]
Debt Instrument [Line Items]
Mortgages payable	22,749	22,942
5.99% Mortgage Note Due May 1, 2026 [Member]
Debt Instrument [Line Items]
Mortgages payable	$ 1,235	$ 1,370

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant