Employee Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension Plan [Member]
Components of net periodic benefit cost
Service cost	$ 344	$ 276
Interest cost	450	473
Expected return on plan assets	(952)	(819)
Recognized net losses	261	229
Net periodic benefit cost (credit)	103	159
Supplemental Insurance/ Retirement Plan [Member]
Components of net periodic benefit cost
Service cost	353	256
Interest cost	466	482
Recognized prior service cost	29	28
Recognized net losses	211	109
Net periodic benefit cost (credit)	$ 1,059	$ 875