Components of Net Periodic Benefit Cost (Benefit Cost (Increase) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0	$ 0
Interest cost	198	250
Expected return on plan assets	(807)	(737)
Amortization of prior service cost	0	0
Amortization of the net loss (gain)	118	174
Net periodic (benefit) increase cost	(491)	(313)
Other post-retirement benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	9	20
Interest cost	106	178
Expected return on plan assets	0	0
Amortization of prior service cost	0	0
Amortization of the net loss (gain)	(268)	(62)
Net periodic (benefit) increase cost	$ (153)	$ 136