Note Pension and postretirement benefits (Components of net periodic pension cost) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 6,120	$ 6,291
Expected return on plan assets	(10,186)	(9,623)
Amortization of net loss (gain)	5,054	4,880
Total net periodic pension (benefit) cost	988	1,548
Other Pension Plans Defined Benefit Member
Defined Benefit Plan Disclosure [Line Items]
Interest cost	352	348
Expected return on plan assets	(502)	(538)
Amortization of net loss (gain)	411	331
Total net periodic pension (benefit) cost	$ 261	$ 141