Fair Value - Schedule of Fair Value of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Financial assets:
Cash and cash equivalents	$ 40,155	$ 42,255
Restricted cash	2,165	1,662	$ 2,568	$ 2,232
Rent and other receivables	2,554	2,141
Financial liabilities:
Dividends payable	1,378	1,362
Accounts payable and accrued expenses	3,291	3,949
Secured revolving credit facility	50,000	50,000
Mortgage notes payable	365,821	366,201
Pension withdrawal liability	890	926
Estimate of Fair Value Measurement [Member]
Financial assets:
Cash and cash equivalents	40,155	42,255
Restricted cash	2,165	1,662
Rent and other receivables	2,554	2,141
Financial liabilities:
Dividends payable	1,378	1,362
Accounts payable and accrued expenses	3,291	3,949
Secured revolving credit facility	50,000	50,000
Pension withdrawal liability	956	1,027
Mortgages [Member]
Financial liabilities:
Mortgage notes payable	365,821	366,201
Mortgages [Member] | Estimate of Fair Value Measurement [Member]
Financial liabilities:
Mortgage notes payable	$ 376,577	$ 377,371