Projected Benefit Obligations, Accumulated Benefit Obligations and Fair Value of Plan Assets for Plans where Accumulated Benefit Obligation Exceeded Fair Value of Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
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	$ 513,444	$ 478,234
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate accumulated benefit Obligation	459,556	431,668
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate fair value of plan assets	374,360	383,683
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	96,754	78,667
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate accumulated benefit Obligation	82,642	69,104
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	114,962	122,879
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate accumulated benefit Obligation	114,962	122,879
Plans where accumulated benefit obligation exceeds fair value of plan assets, Aggregate fair value of plan assets	$ 0	$ 0