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, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	$ (19,871)	$ 20,812
Amendments and curtailments		(30,088)
Amortization of prior service (cost) credit	4,172	802	$ 4,587
Amortization of actuarial (loss) gain	(42,967)	(28,275)	$ (30,205)
Total recognized in other comprehensive income, pre-tax	(58,666)	(36,749)
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	(15,113)	29,323
Amortization of prior service (cost) credit	(557)	(557)
Amortization of actuarial (loss) gain	(43,793)	(29,263)
Total recognized in other comprehensive income, pre-tax	(59,463)	(497)
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	(4,758)	(8,511)
Amendments and curtailments		(30,088)
Amortization of prior service (cost) credit	4,729	1,359
Amortization of actuarial (loss) gain	826	988
Total recognized in other comprehensive income, pre-tax	$ 797	$ (36,252)