Projected Benefit Obligations, Accumulated Benefit Obligations and Fair Value of Plan Assets for Plans where Accumulated Benefit Obligations Exceeded Fair Value of Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Funded Defined Benefit Pension Plans | Qualified Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Plans where accumulated benefit obligation exceeds fair value of plan assets, Projected benefit obligation	$ 587,318	$ 513,444
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate accumulated benefit Obligation	523,773	459,556
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate fair value of plan assets	431,788	374,360
Unfunded Defined Benefit Pension Plans | Non-Qualified Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Plans where accumulated benefit obligation exceeds fair value of plan assets, Projected benefit obligation	112,135	96,754
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate accumulated benefit Obligation	98,498	82,642
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate fair value of plan assets	0	0
Unfunded Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Plans where accumulated benefit obligation exceeds fair value of plan assets, Projected benefit obligation	124,134	114,962
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate accumulated benefit Obligation	124,134	114,962
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate fair value of plan assets	$ 0	$ 0