Significant Accounting Policies - Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Additional interest expense	$ 35,468	$ 23,141	$ 103,526	$ 68,037
Tax benefit	29,089	52,763	84,147	119,277
Earnings from Continuing Operations	4,027	2,140	8,311	6,395
Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations	4,027	1,918	8,031	5,738
Unamortized Value of Terminated Forward Starting Interest Rate Swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Earnings from Continuing Operations		222	280	657
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Settlement expense	2,692		2,692
Prior service credit	(492)	(402)	(1,479)	(1,070)
Actuarial loss	3,153	3,513	9,463	10,370
Tax benefit	(1,326)	(1,193)	(2,645)	(3,562)
Earnings from Continuing Operations	4,027	1,918	8,031	5,738
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	$ 5,353	3,111	10,676	9,300
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		369	458	1,089
Tax benefit		(147)	(178)	(432)
Earnings from Continuing Operations		$ 222	$ 280	$ 657