Retirement Plans - Net Periodic Benefit Cost Recognized for Supplemental Retirement Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net pension cost included the following components:
Service cost-benefits earned during the period	$ 879	$ 973	$ 941
Interest cost on projected benefit obligation	1,131	949	991
Amortization of net obligation at transition	2	2	2
Amortization of prior service cost	(54)	(54)	(12)
Recognized net actuarial loss	408	510	390
Net periodic pension cost	$ 2,366	$ 2,380	$ 2,312