Components of Net Periodic Pension Cost Benefit (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 615	$ 725	$ 689
Interest cost	3,357	4,237	4,063
Expected return on plan assets	(5,261)	(4,558)	(5,197)
Amortization of actuarial loss		1,533
Net periodic cost	$ (1,289)	$ 1,937	$ (445)