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Rental Income - Additional information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Leases [Abstract]        
Lease income $ 198,000 $ 594,000 $ 198,000 $ 594,000