Retirement and Postretirement Benefit Plans - Net Periodic Benefit Cost Components (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement loss recognized	$ 500
Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	687	$ 1,097
Expected return on plan assets	(1,916)	(1,855)
Amortization of net loss	850	581
Settlement loss recognized	500
Net periodic benefit cost (credit)	121	(177)
Other Post Retirement Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	19	17
Interest cost	68	107
Amortization of prior service cost	11	11
Amortization of net loss		(2)
Net periodic benefit cost (credit)	$ 98	$ 133