Note Pension and postretirement benefits (Components of net periodic benefit cost) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plans
Personnel costs:
Service cost	$ 0	$ 0
Other operating expenses
Interest cost	7,110	6,373
Expected return on plan assets	(8,096)	(10,060)
Amortization of prior service cost (credit)	0	0
Amortization of net loss	5,876	5,065
Total net periodic pension cost	4,890	1,378
OPEB Plan
Personnel costs:
Service cost	190	257
Other operating expenses
Interest cost	1,489	1,390
Expected return on plan assets	0	0
Amortization of prior service cost (credit)	0	(867)
Amortization of net loss	0	321
Total net periodic pension cost	$ 1,378	$ 1,101