Components of Net Periodic Benefit Cost (Benefit Cost (Increase) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	198	250	594	750
Expected return on plan assets	(807)	(737)	(2,421)	(2,211)
Amortization of prior service cost	0	0	0	0
Amortization of the net loss (gain)	118	174	354	522
Net periodic (decrease) increase in benefit cost	(491)	(313)	(1,473)	(939)
Other post-retirement benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	8	19	26	59
Interest cost	106	178	318	534
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of the net loss (gain)	(267)	(62)	(803)	(186)
Net periodic (decrease) increase in benefit cost	$ (153)	$ 135	$ (459)	$ 407