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Components of Net Pension Costs (Detail) (Pension Plans, USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Pension Plans
   
Defined Benefit Plan Disclosure [Line Items]    
Service cost for benefits earned during the year $ 6,249 $ 5,606
Interest cost on accumulated benefit obligation 3,991 3,700
Expected return on assets (3,751) (3,027)
Net amortization of unrecognized amounts, Prior service cost 1,560 1,498
Net amortization of unrecognized amounts, Actuarial loss 1,502 1,229
Net Benefit Costs $ 9,551 $ 9,006