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, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	$ 14,183	$ 24,200
Amendments and curtailments	(28,308)
Amortization of prior service credit	4,587	7,364	$ 7,911
Amortization of actuarial loss	(30,205)	(44,931)	$ (14,494)
Total recognized in other comprehensive income, pre-tax	(39,743)	(13,367)
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	24,736	26,631
Amendments and curtailments	(28,308)
Amortization of prior service credit	3,228	6,005
Amortization of actuarial loss	(30,145)	(44,825)
Total recognized in other comprehensive income, pre-tax	(30,489)	(12,189)
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Net loss (gain)	(10,553)	(2,431)
Amortization of prior service credit	1,359	1,359
Amortization of actuarial loss	(60)	(106)
Total recognized in other comprehensive income, pre-tax	$ (9,254)	$ (1,178)