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Components of Net Periodic Pension Benefit Costs (Detail) (Pension Benefits, USD $)
In Thousands
3 Months Ended9 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2011
Sep. 30, 2010
Pension Benefits
    
Defined Benefit Plan Disclosure [Line Items]    
Service cost$ 2,925$ 3,293$ 10,435$ 10,078
Interest cost7,1627,15121,47721,171
Expected return on plan assets(10,213)(9,375)(30,613)(26,168)
Amortization of prior service cost5125161,5331,549
Amortization of actuarial losses2,1052,1006,0906,299
Curtailment gain(449) (449) 
Net periodic benefit (credit) cost$ 2,042$ 3,685$ 8,473$ 12,929