Benefit Plans - Defined Benefit Pension Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Service cost – benefits earned during year	$ 623	$ 568	$ 1,239	$ 1,136
Interest cost on projected benefit obligation	852	1,121	1,694	2,242
Expected return on plan assets	(2,794)	(2,594)	(5,557)	(5,188)
Amortization of prior service cost	(9)	(9)	(17)	(18)
Amortization of net loss	682	794	1,357	1,587
Net periodic pension income	$ (646)	$ (120)	$ (1,284)	$ (241)