Pension Plans and Other Postretirement Benefits - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	$ 126,618	$ (19,871)
Amortization of prior service (cost) credit	4,173	4,172	$ 802
Amortization of actuarial (loss) gain	(20,745)	42,967	$ (28,275)
Total recognized in other comprehensive income, pre-tax	110,046	58,666
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	127,305	(15,113)
Amortization of prior service (cost) credit	(557)	(557)
Amortization of actuarial (loss) gain	(21,992)	43,793
Total recognized in other comprehensive income, pre-tax	104,756	59,463
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	(687)	(4,758)
Amortization of prior service (cost) credit	4,730	4,729
Amortization of actuarial (loss) gain	1,247	(826)
Total recognized in other comprehensive income, pre-tax	$ 5,290	$ (797)