Fair Values of Pension Plan Assets (Parenthetical) (Detail)
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Dec. 31, 2011
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Mutual Funds | Equity
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Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items] | |
Percentage of investments | 50.00% |
Mutual Funds | Fixed Income Investments
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|
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items] | |
Percentage of investments | 50.00% |
Common Collective Trusts | Equity
|
|
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items] | |
Percentage of investments | 65.00% |
Common Collective Trusts | Fixed Income Investments
|
|
Schedule of Pension and Other Postretirment Benefits Changes in Benefit Obligation and Fair Value of Plan Assets [Line Items] | |
Percentage of investments | 35.00% |