Benefit Plans - Components of Net Periodic Plan Cost for Retirement Plan (Detail) - Director's Retirement Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 22	$ 18	$ 14
Interest cost	16	17	22
Amortization of gain	0	0	(2)
Net periodic postretirement cost	$ 38	$ 35	$ 34