Significant Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense	$ 32,971	$ 24,045	$ 68,059	$ 44,896
Tax benefit	52,601	51,986	55,058	66,514
Earnings from Continuing Operations	2,078	2,130	4,284	4,255
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	2,008	1,910	4,004	3,820
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	70	220	280	435
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service credit	(400)	(358)	(985)	(716)
Actuarial loss	3,069	3,452	6,308	6,905
Tax benefit	(661)	(1,184)	(1,319)	(2,369)
Earnings from Continuing Operations	2,008	1,910	4,004	3,820
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans | Other Nonoperating Income, Net
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications out of accumulated other comprehensive loss before taxes	2,669	3,094	5,323	6,189
Reclassification out of Accumulated Other Comprehensive Income | Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense	111	364	458	720
Tax benefit	(41)	(144)	(178)	(285)
Earnings from Continuing Operations	$ 70	$ 220	$ 280	$ 435