Note Pension and postretirement benefits (Components of net periodic pension cost) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 6,120	$ 6,291	$ 18,359	$ 18,873
Expected return on plan assets	(10,186)	(9,623)	(30,557)	(28,869)
Amortization of net loss (gain)	5,053	4,881	15,160	14,640
Total net periodic pension (benefit) cost	987	1,549	2,962	4,644
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Interest cost	352	348	1,057	1,044
Expected return on plan assets	(502)	(538)	(1,508)	(1,614)
Amortization of net loss (gain)	411	332	1,233	996
Total net periodic pension (benefit) cost	$ 261	$ 142	$ 782	$ 426