Note Pension and postretirement benefits (Components of net periodic postretirement benefit cost) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension and Other Postretirement Benefits Disclosure [Line Items]
Amortization of prior service cost	$ (950)	$ (950)	$ (1,900)	$ (1,900)
Other Postretirement Benefit Plans Defined Benefit [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Service cost	289	368	578	735
Interest cost	1,505	1,589	3,010	3,178
Amortization of prior service cost	(950)	(950)	(1,900)	(1,900)
Amortization of net loss (gain)	275	249	550	498
Total net periodic pension cost	$ 1,119	$ 1,256	$ 2,238	$ 2,511