Significant Accounting Policies - Changes in Accumulated Other Comprehensive Loss Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 5,097,270	$ 4,855,470	$ 4,949,412	$ 4,682,477
Other comprehensive earnings (loss), net of tax	2,569	4,392	8,814	7,613
Ending Balance	5,304,438	4,942,328	5,304,438	4,942,328
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(136,021)	(124,798)	(141,505)	(128,802)
Amounts reclassified from accumulated other comprehensive loss, net of tax	2,726	4,027	8,210	8,031
Other comprehensive earnings (loss), net of tax		4,027		8,031
Ending Balance	(133,295)	(120,771)	(133,295)	(120,771)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,313)	(1,085)	(2,074)	(22)
Other comprehensive earnings (loss) before reclassifications, net of tax		365		(698)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(157)		604
Other comprehensive earnings (loss), net of tax		365		(698)
Ending Balance	(1,470)	(720)	(1,470)	(720)
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				(280)
Amounts reclassified from accumulated other comprehensive loss, net of tax				280
Other comprehensive earnings (loss), net of tax				280
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(137,334)	(125,883)	(143,579)	(129,104)
Other comprehensive earnings (loss) before reclassifications, net of tax		365		(698)
Amounts reclassified from accumulated other comprehensive loss, net of tax	2,569	4,027	8,814	8,311
Other comprehensive earnings (loss), net of tax		4,392		7,613
Ending Balance	$ (134,765)	$ (121,491)	$ (134,765)	$ (121,491)