Note Pension and postretirement benefits (Components of net periodic postretirement benefit cost) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension and Other Postretirement Benefits Disclosure [Line Items]
Amortization of prior service cost	$ (950)	$ (950)
Other Postretirement Benefit Plans Defined Benefit [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Service cost	289	368
Interest cost	1,505	1,589
Amortization of prior service cost	(950)	(950)
Amortization of net loss (gain)	275	249
Total net periodic pension cost	$ 1,119	$ 1,256