Leases - Additional Information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) Property	Jun. 30, 2019 USD ($) Property CorporateOfficeLease
Corporate Office Leases [Member]
Operating Leased Assets [Line Items]
Number of operating leases | CorporateOfficeLease		9
Lease termination date		Jan. 31, 2022
Amount incurred for leased office space | $	$ 0.7	$ 1.3
Ground Leases [Member]
Operating Leased Assets [Line Items]
Unsecured borrowing rates for actual pricing period used for calculating discount rate		30 years
Number of operating properties | Property	14	14
Minimum [Member] | Corporate Office Leases [Member]
Operating Leased Assets [Line Items]
Discount rate	3.30%	3.30%
Remaining lease terms	1 year	1 year
Minimum [Member] | Ground Leases [Member]
Operating Leased Assets [Line Items]
Discount rate	4.40%	4.40%
Operating lease expiration year		2042
Maximum [Member] | Corporate Office Leases [Member]
Operating Leased Assets [Line Items]
Discount rate	3.90%	3.90%
Remaining lease terms	10 years	10 years
Maximum [Member] | Ground Leases [Member]
Operating Leased Assets [Line Items]
Discount rate	5.50%	5.50%
Operating lease expiration year		2113
Residential Apartment Leases [Member]
Operating Leased Assets [Line Items]
Percentage of rental income		97.10%
Retail Commercial Leases [Member]
Operating Leased Assets [Line Items]
Percentage of rental income		2.90%
Retail Commercial Leases [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Retail/commercial leases term	5 years	5 years
Retail Commercial Leases [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Retail/commercial leases term	10 years	10 years