Benefit Plans - Additional Information (Detail) - USD ($)	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	$ 623,000	$ 568,000	$ 1,239,000	$ 1,136,000
Periodic pension income			2,500,000	$ 1,400,000
Minimum required pension plan contribution	5,200,000		5,200,000
Available credit balance	$ 64,200,000		64,200,000
Expected voluntary contribution for the year 2021			$ 0