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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 48	$ 373	$ 92	$ 857
Interest cost	300	3,337	601	6,787
Expected return on plan assets		(3,699)		(7,395)
Amortization of prior service cost/(credit)	11	54	23	88
Amortization of unrecognized/actuarial loss (gain)	161	789	321	1,564
Total net periodic benefit cost/(credit)	520	854	1,037	1,901
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	9	14	18
Interest cost	46	84	92	168
Amortization of prior service cost/(credit)	(116)	(3)	(232)	(5)
Amortization of unrecognized/actuarial loss (gain)	(208)	(173)	(417)	(346)
Total net periodic benefit cost/(credit)	$ (271)	$ (83)	$ (543)	$ (165)