Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Ground	Dec. 31, 2017 USD ($)	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	64 months
Depreciation commencement description	Depreciation on development buildings 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.
Threshold percentage to recognize gain or loss on transactions in consolidated entities	100.00%
Percentage of taxable income distribute	100.00%
Capitalized cost	$ 21.2	$ 23.8	$ 23.9
Number of ground and office space leases | Ground	130
Operating lease, asset	$ 400.0
Operating lease, liability	$ 400.0
Weighted average remaining lease term	27 years 10 months 24 days
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