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Retirement Benefit Obligations - Additional Information (Detail) (USD $) | 6 Months Ended
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Jun. 30, 2012
Defined Benefit Plan Disclosure [Line Items] |
Contributions to Pension plan | $ 6,300,000
Supplemental Employee Retirement Plans, Defined Benefit |
Defined Benefit Plan Disclosure [Line Items] |
Contributions to Pension plan | 26,000
Expected additional contribution to SERP plan | $ 27,000

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