Leases - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) option	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) option	Jun. 30, 2018 USD ($)
Lessor, Lease, Description [Line Items]
Number of extension options (option) | option	1		1
Lessee, operating lease, renewal term (years)	10 years		10 years
Right-of-use asset	$ 4,796		$ 4,796
Lease liability	$ 5,139		$ 5,139
Weighted average discount rate (percentage)	4.20%		4.20%
Operating leases, rent expense	$ 187	$ 187	$ 373	$ 373
Cash paid for rent expense	$ 200	$ 200	$ 400	$ 400
Minimum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	5 years		5 years
Maximum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	25 years		25 years
Alexander Apartment Tower | Minimum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	1 year		1 year
Alexander Apartment Tower | Maximum
Lessor, Lease, Description [Line Items]
Lessor, operating lease, term (years)	2 years		2 years