Components of Net Periodic Benefit Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 26,346	$ 23,500	$ 22,406
Interest cost	30,903	29,869	30,785
Expected return on plan assets	(28,974)	(25,826)	(25,919)
Amortization of prior service cost (credit)	1,006	1,254	1,314
Amortization of transitional (asset) liability	(514)	(529)	(536)
Recognized actuarial loss	17,338	16,389	12,484
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	46,105	44,657	40,534
Termination benefits expense	849	6,177	695
Curtailment expense (benefit)	1,365	0	1,036
Net periodic benefit expense	48,319	50,834	42,265
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4,566	3,958	4,547
Interest cost	5,189	5,174	6,141
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(143)	(173)	(240)
Amortization of transitional (asset) liability	8	8	8
Recognized actuarial loss	1,484	1,317	2,329
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	11,104	10,284	12,785
Termination benefits expense	0	0	0
Curtailment expense (benefit)	(442)	0	(605)
Net periodic benefit expense	$ 10,662	$ 10,284	$ 12,180