Changes in Accumulated Other Comprehensive Earnings (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 4,142,590
Other comprehensive earnings before reclassifications, net of tax	137	$ 115
Amounts reclassified from accumulated other comprehensive earnings, net of tax	2,125	1,674
Other comprehensive earnings, net of tax	2,262	1,789
Ending Balance	4,075,954	3,945,636
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(128,373)	(103,380)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	1,910	1,473
Other comprehensive earnings, net of tax	1,910	1,473
Ending Balance	(126,463)	(101,907)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,162)	(264)
Other comprehensive earnings before reclassifications, net of tax	137	115
Other comprehensive earnings, net of tax	137	115
Ending Balance	(1,025)	(149)
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,152)	(1,978)
Amounts reclassified from accumulated other comprehensive earnings, net of tax	215	201
Other comprehensive earnings, net of tax	215	201
Ending Balance	(937)	(1,777)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(130,687)	(105,622)
Ending Balance	$ (128,425)	$ (103,833)