Retirement Plans and Other Post-Retirement Benefits - Schedule of Net Periodic Benefit (Income) Expense of Pension and Other Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Pension settlement charge	$ 6,154	$ 75,326
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		1,300	$ 2,300
Interest cost	1,200	11,500	13,300
Expected return on plan assets		(13,700)	(21,100)
Amortization of prior service cost/(credit)		200
Amortization of actuarial loss	700	2,800	7,100
Termination benefits		1,300
Pension settlement charge	(2,300)	75,300
Total net periodic benefit (income) expense	1,900	78,700	1,600
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			100
Interest cost	200	300	500
Amortization of prior service cost/(credit)	(500)
Amortization of actuarial loss	(800)	(900)	(300)
Total net periodic benefit (income) expense	$ (1,100)	$ (600)	$ 300