Long Term Lease Obligations - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Leases Disclosure [Line Items]
Number of properties subject to noncancelable long-term lease | property	0
Minimum rental obligations	$ 10,500	$ 159,000	$ 176,000
Rent expense	$ 774,700	$ 843,300	$ 904,900
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%
Flagship Center
Leases Disclosure [Line Items]
Number of developed parcels | property	2