Estimated Amount that will be Amortized from Accumulated Other Comprehensive Income into Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ (354)	$ 993
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	10,308
Total estimated 2012 amortization	10,308
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (benefit)	(27)
Net actuarial (gain) loss	(3,306)
Total estimated 2012 amortization	$ (3,333)

The amounts in accumulated other comprehensive income related to gains and losses that are not recognized immediately and are expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

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The amounts in accumulated other comprehensive income related to prior service cost or credit expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

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- Definition

The aggregate amount in accumulated other comprehensive income expected to be recognized as a component of net periodic benefit cost over the fiscal year that follows the most recent annual statement of financial position presented, including the net gain (loss), net prior service cost or credit, and net transition asset or obligation.

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