Components of Net Periodic Benefit Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 22,406	$ 20,706	$ 17,052
Interest cost	30,785	30,144	28,767
Expected return on plan assets	(25,919)	(24,199)	(20,375)
Amortization of prior service cost	1,314	1,558	1,635
Amortization of transitional asset (liability)	(536)	(514)	(466)
Recognized actuarial loss	12,484	12,257	10,305
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	40,534	39,952	36,918
Termination benefits expense	695	0	1,867
Curtailment expense	1,036	0	575
Net periodic benefit expense	42,265	39,952	39,360
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	4,547	4,133	3,121
Interest cost	6,141	6,211	5,688
Expected return on plan assets	0	0	0
Amortization of prior service cost	(240)	(263)	(263)
Amortization of transitional asset (liability)	8	8	0
Recognized actuarial loss	2,329	2,790	1,551
Defined Benefit Plan, Gross Periodic Benefit Cost, Total	12,785	12,879	10,097
Termination benefits expense	0	0	0
Curtailment expense	(605)	0	397
Net periodic benefit expense	$ 12,180	$ 12,879	$ 10,494