Schedule of Maturities of lease liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
2019	$ 356
2019		$ 474
2020	475	474
2021	475	474
2022	475	474
2023	475	474
Later years	25,640	25,582
Total undiscounted lease payments	27,896	$ 27,952
less imputed interest	19,048
Ground lease liabilities	$ 8,848