Note Other comprehensive income (loss) (Disclosure of accumulated other comprehensive income (loss)) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Foreign Currency Translation
Beginning Balance	[1]	$ (42,941)	$ (39,817)	$ (43,034)	$ (39,956)
Other comprehensive loss before reclassifications	[1]	(3,456)	(1,588)	(3,363)	(1,449)
Net change	[1]	(3,456)	(1,588)	(3,363)	(1,449)
Ending Balance	[1]	(46,397)	(41,405)	(46,397)	(41,405)
Adjustment of pension and postretirement benefit plans
Beginning Balance	[1]	(202,652)	(208,769)	(205,408)	(211,610)
Amounts reclassified from accumulated other comprehensive income (loss) for amortization of net losses	[1]	3,286	3,421	6,571	6,842
Amounts reclassified from accumulated other comprehensive income (loss) for amortization of prior service credit	[1]	(529)	(580)	(1,058)	(1,160)
Net change	[1]	2,757	2,841	5,513	5,682
Ending Balance	[1]	(199,895)	(205,928)	(199,895)	(205,928)
Unrealized net holding losses on debt securities
Beginning Balance	[1]	(217,179)	(71,707)	(102,775)	(69,003)
Other comprehensive (loss) income before reclassifications	[1]	(33,243)	8,553	(147,647)	5,849
Other-than-temporary impairment amounts reclassified from accumulated other comprehensive (loss) income	[1]	0	6,740	0	6,740
Net change	[1]	(33,243)	15,293	(147,647)	12,589
Ending Balance	[1]	(250,422)	(56,414)	(250,422)	(56,414)
Unrealized holding gains on equity securities
Beginning Balance		0	650	605	685
Reclassification to retained earnings due to cumulative effect of accounting change	[1]	0	0	(605)	0
Other comprehensive income before reclassifications	[1]	0	37	0	132
Amounts reclassified from accumulated other comprehensive income	[1]	0	(15)	0	(145)
Net change	[1]	0	22	(605)	(13)
Ending Balance		0	672	0	672
Unrealized net (losses) gain on cash flow hedges
Beginning Balance	[1]	(66)	(269)	(40)	(402)
Other comprehensive (loss) income before reclassifications	[1]	(165)	(230)	582	(619)
Amounts reclassified from other accumulated other comprehensive (loss) income	[1]	153	631	(620)	1,153
Net change	[1]	(12)	401	(38)	534
Ending Balance	[1]	(78)	132	(78)	132
Accumulated other comprehensive (loss) income	[1]	$ (496,792)	$ (302,943)	$ (496,792)	$ (302,943)	$ (350,652)

[1] All amounts presented are net of tax.