Note Pension and postretirement benefits (Components of net periodic pension cost) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Amortization of net losses	$ (5,386)	$ (5,607)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	6,029	6,120
Expected return on plan assets	(9,551)	(10,186)
Amortization of net losses	4,716	5,054
Net periodic pension cost (benefit)	1,194	988
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Interest cost	344	352
Expected return on plan assets	(509)	(502)
Amortization of net losses	349	411
Net periodic pension cost (benefit)	$ 184	$ 261