Significant Accounting Policies - Changes in Accumulated Other Comprehensive Earnings Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 4,949,412	$ 4,682,477
Other comprehensive earnings (loss) before reclassifications, net of tax	497	(587)
Amounts reclassified from accumulated other comprehensive loss, net of tax	2,758	2,206
Other comprehensive earnings (loss), net of tax	3,255	1,619
Ending Balance	4,975,496	4,679,830
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(141,505)	(128,802)
Amounts reclassified from accumulated other comprehensive loss, net of tax	2,758	1,996
Other comprehensive earnings (loss), net of tax	2,758	1,996
Ending Balance	(138,747)	(126,806)
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2,074)	(22)
Other comprehensive earnings (loss) before reclassifications, net of tax	497	(587)
Other comprehensive earnings (loss), net of tax	497	(587)
Ending Balance	(1,577)	(609)
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		210
Other comprehensive earnings (loss), net of tax		210
Ending Balance		(70)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(143,579)	(129,104)
Ending Balance	$ (140,324)	$ (127,485)