Changes in Accumulated Other Comprehensive Earnings (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 4,142,590
Other comprehensive earnings (loss) before reclassifications, net of tax	$ 389	$ (3,968)	526	$ (3,947)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	2,130	1,733	4,255	3,501
Other comprehensive (loss) earnings, net of tax	2,519	(2,235)	4,781	(446)
Ending Balance	4,200,531	4,016,500	4,200,531	4,016,500
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(126,463)	(101,907)	(128,373)	(103,380)
Other comprehensive earnings (loss) before reclassifications, net of tax		(3,736)		(3,830)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	1,910	1,529	3,820	3,096
Other comprehensive (loss) earnings, net of tax	1,910	(2,207)	3,820	(734)
Ending Balance	(124,553)	(104,114)	(124,553)	(104,114)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,025)	(149)	(1,162)	(264)
Other comprehensive earnings (loss) before reclassifications, net of tax	389	(232)	526	(117)
Other comprehensive (loss) earnings, net of tax	389	(232)	526	(117)
Ending Balance	(636)	(381)	(636)	(381)
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(937)	(1,777)	(1,152)	(1,978)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	220	204	435	405
Other comprehensive (loss) earnings, net of tax	220	204	435	405
Ending Balance	(717)	(1,573)	(717)	(1,573)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(128,425)	(103,833)	(130,687)	(105,622)
Ending Balance	$ (125,906)	$ (106,068)	$ (125,906)	$ (106,068)