Retirement Plans and Other Post-Retirement Benefits - Schedule of Defined Benefit Plan Weighted-Average Assumptions Used in Computing Net Periodic Benefit Expense (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit expense	2.70%	4.34%	3.85%
Future compensation growth rate		2.50%	3.00%
Expected long-term rate of return on plan assets		4.50%	7.25%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate - benefit expense	3.11%	4.19%	3.68%