Leases - Lessee Accounting (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) tenant renewalOption	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Lessor, number of tenants | tenant	2
Right-of-use asset	$ 2,618	$ 2,652
Lease liability	$ 2,675	$ 2,674
Ground Lease | Yonkers, NY
Lessee, Lease, Description [Line Items]
Number of renewal options | renewalOption	1
Renewal term option	21 years
Remaining term	24 years
Corporate Office | Great Neck, NY
Lessee, Lease, Description [Line Items]
Renewal term option	5 years
Remaining term	15 years 3 months 18 days