Employee Benefit Plans - Expected Cash Flows for Pension Plans and Other Postretirement Benefit Plans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 70,099
Defined Benefit Plan, Expected Future Benefit Payments in Year One	76,390
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	86,670
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	91,697
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	97,333
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	103,708
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	612,723
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	1,122
Defined Benefit Plan, Expected Future Benefit Payments in Year One	1,122
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	965
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	824
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	644
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	451
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 1,232