Retirement Plans - Net Periodic Benefit Cost Recognized for Supplemental Retirement Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net pension cost included the following components:
Service cost-benefits earned during the period	$ 2,225	$ 879	$ 973
Interest cost on projected benefit obligation	1,014	1,131	949
Amortization of net obligation at transition	1	2	2
Amortization of prior service cost	(55)	(54)	(54)
Recognized net actuarial loss	9,309	408	510
Net periodic pension cost	$ 12,494	$ 2,366	$ 2,380