Components of Net Periodic Benefit Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 23,500	$ 22,406	$ 20,706
Interest cost	29,869	30,785	30,144
Expected return on plan assets	(25,826)	(25,919)	(24,199)
Amortization of prior service cost (credit)	1,254	1,314	1,558
Amortization of transitional (asset) liability	(529)	(536)	(514)
Recognized actuarial loss	16,389	12,484	12,257
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	44,657	40,534	39,952
Termination benefits expense	6,177	695	0
Curtailment expense	0	1,036	0
Net periodic benefit expense	50,834	42,265	39,952
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	3,958	4,547	4,133
Interest cost	5,174	6,141	6,211
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	(173)	(240)	(263)
Amortization of transitional (asset) liability	8	8	8
Recognized actuarial loss	1,317	2,329	2,790
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	10,284	12,785	12,879
Termination benefits expense	0	0	0
Curtailment expense	0	(605)	0
Net periodic benefit expense	$ 10,284	$ 12,180	$ 12,879