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Retirement Benefit Plans - Assumed Health Care Cost Trend Rates (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]  
Aggregated service and interest cost, 1% Decrease in Rates $ 1,332
Postretirement benefit obligation, 1% Decrease in Rates 33,476
Aggregated service and interest cost, Assumed Rates 1,529
Postretirement benefit obligation, Assumed Rates 37,831
Aggregated service and interest cost, 1% Increase in Rates 1,774
Postretirement benefit obligation, 1% Increase in Rates $ 43,115