Note Other comprehensive income (loss) (Disclosure of accumulated other comprehensive income (loss)) (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Foreign Currency Translation
Beginning Balance	[1]	$ (41,405)	$ (38,070)	$ (39,956)	$ (35,930)
Other comprehensive loss before reclassifications	[1]	(390)	(325)	(1,839)	(2,465)
Net change	[1]	(390)	(325)	(1,839)	(2,465)
Ending Balance	[1]	(41,795)	(38,395)	(41,795)	(38,395)
Adjustment of pension and postretirement benefit plans
Beginning Balance	[1]	(205,928)	(205,743)	(211,610)	(211,276)
Amounts reclassified from accumulated other comprehensive income (loss) for amortization of net losses	[1]	3,421	3,348	10,263	10,041
Amounts reclassified from accumulated other comprehensive income (loss) for amortization of prior service credit	[1]	(580)	(580)	(1,740)	(1,740)
Net change	[1]	2,841	2,768	8,523	8,301
Ending Balance	[1]	(203,087)	(202,975)	(203,087)	(202,975)
Unrealized net holding (losses) gain on investments
Beginning Balance	[1]	(55,742)	98,761	(68,318)	(9,560)
Other comprehensive (loss) income before reclassification	[1]	9,350	(14,131)	15,331	94,023
Other-than-temporary impairment amounts reclassified from accumulated other comprehensive (loss) income	[1]	0	0	6,740	167
Amounts reclassified from accumulated other comprehensive (loss) income	[1]	(82)	(316)	(227)	(316)
Net change	[1]	9,268	(14,447)	21,844	93,874
Ending Balance	[1]	(46,474)	84,314	(46,474)	84,314
Unrealized net (losses) gain on cash flow hedges
Beginning Balance	[1]	132	(560)	(402)	(120)
Other comprehensive (loss) income before reclassifications	[1]	(250)	(685)	(869)	(2,843)
Amounts reclassified from other accumulated other comprehensive (loss) income	[1]	142	1,006	1,295	2,724
Net change	[1]	(108)	321	426	(119)
Ending Balance	[1]	24	(239)	24	(239)
Accumulated other comprehensive (loss) income	[1]	$ (291,332)	$ (157,295)	$ (291,332)	$ (157,295)	$ (320,286)

[1] All amounts presented are net of tax.