Retirement Plans and Other Post-Retirement Benefits - Schedule of Net Periodic Costs of Pension and Post Retirement Medical Benefit Plans Included in Continuing Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 44
Interest cost	$ 250	301
Amortization of prior service cost/(credit)	12	12
Amortization of actuarial loss (gain)	199	160
Total net periodic benefit expense/(income)	461	517
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	7
Interest cost	32	46
Amortization of prior service cost/(credit)	(58)	(116)
Amortization of actuarial loss (gain)	12	(209)
Total net periodic benefit expense/(income)	$ (7)	$ (272)