Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Ground	Dec. 31, 2016 USD ($)
Schedule Of Significant Accounting Policies [Line Items]
Consolidation percentage if not wholly owned but controlled	Less than 100% of the equity
Percentage of occupancy for stabilization	90.00%
Period after completion of construction for commencement of depreciation	1 year
Estimated useful lives	40 years
Weighted average lease term period	54 months
Depreciation commencement description	Depreciation commences when the asset is ready for its intended use, which we define as the earlier of stabilization (90% occupied) or one year after completion of construction.
Noncontrolling interests in real estate entities	100.00%
Percentage of taxable income distribute	100.00%
Capitalized cost | $	$ 23.8	$ 23.9
Number of ground and office space leases | Ground	88
Capital Improvements [Member] | Minimum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives	5 years
Capital Improvements [Member] | Maximum [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives	7 years
Standard Tenant Improvements [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives	10 years
Depreciable and Land Improvements [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives	25 years
Operating Properties [Member]
Schedule Of Significant Accounting Policies [Line Items]
Estimated useful lives	30 years