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Components of Postretirement Benefits Expense (Income) (Detail) (Postretirement Benefits, USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Postretirement Benefits
     
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 274 $ 263 $ 382
Interest cost 3,172 3,393 3,564
Expected return on assets (488) (509) (526)
Actuarial loss 3,161 3,324 763
Amortization of prior service benefit (95) (697) (1,704)
Benefits expense $ 6,024 $ 5,774 $ 2,479
Weighted-average assumption percentages:      
Discount rate 5.10% 5.30% 5.70%
Expected return on plan assets 7.00% 7.00% 7.00%
Rate of compensation increase 4.00% 4.00% 4.00%