Reconciliation of Asset Retirement Obligations which are Included in Other Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of period	$ 4,934	$ 4,314
Changes in estimates	33	(2)
Liabilities incurred	121	290
Liabilities settled	0	(67)
Acquisitions of properties	(16)	(83)
Accretion expense	357	316
Balance at end of period	$ 5,461	$ 4,934