Long-Term Lease Obligations - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)
Leases Disclosure [Line Items]
Number of properties subject to noncancelable long-term lease | property	0	0
Rent expense	$ 799,300	$ 806,500
Rent expense			$ 779,800
Flagship Center
Leases Disclosure [Line Items]
Number of developed parcels | property	2
90-year Ground Leasehold Interest
Leases Disclosure [Line Items]
Ground leasehold interest period	90 years
Minimum annual lease rent over lease term	$ 1
99-year Ground Lease
Leases Disclosure [Line Items]
Ground leasehold interest period	99 years
Minimum annual lease rent over lease term	$ 1
Percent of underlying land held under a 99-year ground lease	3.40%