Note Pension and postretirement benefits (Components of net periodic pension cost) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Amortization of net losses	$ (5,385)	$ (5,606)	$ (10,771)	$ (11,213)
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	6,029	6,120	12,058	12,240
Expected return on plan assets	(9,551)	(10,186)	(19,101)	(20,372)
Amortization of net losses	4,715	5,053	9,431	10,107
Total net periodic pension cost (benefit)	1,193	987	2,388	1,975
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Interest cost	344	352	688	705
Expected return on plan assets	(509)	(502)	(1,018)	(1,005)
Amortization of net losses	349	411	699	822
Total net periodic pension cost (benefit)	$ 184	$ 261	$ 369	$ 522