Commitments and Contingencies - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Ground lease commitments, 2019	$ 1,225,000
Ground lease commitments, 2020	1,262,000
Ground lease commitments, 2021	1,299,000
Ground lease commitments, 2022	1,338,000
Ground lease commitments, 2023	1,379,000
Ground lease commitments, Thereafter	11,450,000
New York, NY [Member] \| Ground Lease [Member]
Property, Plant and Equipment [Line Items]
Ground lease commitments, 2019	1,844,000
Ground lease commitments, 2020	1,900,000
Ground lease commitments, 2021	1,957,000
Ground lease commitments, 2022	2,015,000
Ground lease commitments, 2023	2,076,000
Ground lease commitments, Thereafter	$ 97,836,000
Expiration date	Jun. 01, 2053
Chicago, IL [Member] \| Ground Lease [Member]
Property, Plant and Equipment [Line Items]
Ground lease commitments, 2019	$ 440,000
Ground lease commitments, 2020	440,000
Ground lease commitments, 2021	440,000
Ground lease commitments, 2022	440,000
Ground lease commitments, 2023	440,000
Ground lease commitments, Thereafter	$ 4,727,000
Expiration date	Sep. 19, 2034

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

No definition available.

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- Definition

Future rental payments receivable within one year of the balance sheet date under an operating lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164653&loc=d3e41551-112718

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Future rental payments receivable within the fifth year from the balance sheet date under an operating lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Definition

Future rental payments receivable within the fourth year from the balance sheet date under an operating lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Definition

Future rental payments receivable within the third year from the balance sheet date under an operating lease.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Future rental payments receivable within the second year from the balance sheet date under an operating lease.

+ References

+ Details

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

- Definition

Future minimum lease payments receivable under operating leases for periods greater than five years following the balance sheet date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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- Definition

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.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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