Changes in Accumulated Other Comprehensive Earnings (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 4,142,590
Other comprehensive earnings (loss) before reclassifications, net of tax	$ 838	$ (198)	1,364	$ (4,145)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	2,140	1,755	6,395	5,256
Other comprehensive earnings (loss), net of tax	2,978	1,557	7,759	1,111
Ending Balance	4,333,982	4,158,398	4,333,982	4,158,398
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(124,553)	(104,114)	(128,373)	(103,380)
Other comprehensive earnings (loss) before reclassifications, net of tax				(3,830)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	1,918	1,547	5,738	4,643
Other comprehensive earnings (loss), net of tax	1,918	1,547	5,738	813
Ending Balance	(122,635)	(102,567)	(122,635)	(102,567)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(636)	(381)	(1,162)	(264)
Other comprehensive earnings (loss) before reclassifications, net of tax	838	(198)	1,364	(315)
Other comprehensive earnings (loss), net of tax	838	(198)	1,364	(315)
Ending Balance	202	(579)	202	(579)
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(717)	(1,573)	(1,152)	(1,978)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	222	208	657	613
Other comprehensive earnings (loss), net of tax	222	208	657	613
Ending Balance	(495)	(1,365)	(495)	(1,365)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(125,906)	(106,068)	(130,687)	(105,622)
Ending Balance	$ (122,928)	$ (104,511)	$ (122,928)	$ (104,511)