Components of Net Periodic Benefit Cost (Benefit Cost (Increase) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	250	300	500	600
Expected return on plan assets	(737)	(641)	(1,474)	(1,282)
Amortization of prior service cost	0	0	0	0
Amortization of the net loss (gain)	174	254	348	508
Net periodic (decrease) increase in benefit cost	(313)	(87)	(626)	(174)
Other post-retirement benefits
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	20	20	40	40
Interest cost	178	209	356	419
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	0	0	0
Amortization of the net loss (gain)	(62)	(207)	(124)	(414)
Net periodic (decrease) increase in benefit cost	$ 136	$ 22	$ 272	$ 45