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Retirement Plans - Additional Information (Detail) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Employer contribution | 3.00% |  |  |
Employee contribution | 80.00% |  |  |
Contribution of employee matched with employer's contribution | 4.00% |  |  |
Contribution matched to employer's contribution | 50.00% |  |  |
Plan expense | $ 2,600,000 | $ 2,500,000 | $ 2,600,000 |
Commonwealth compensation to plan |  |  |  | 4.00%
Commonwealth compensation to plan, additional |  |  |  | 3.00%
Retirement Plan expense | $ 0 | $ 86,000 | $ 96,000 |
Minimum [Member] |  |  |  |
Eligibility of participants | 1.00% |  |  |
Maximum [Member] |  |  |  |
Eligibility of participants | 25.00% |  |  |

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- Definition Deferred Compensation Plan Net Of Contribution Expenses + References No definition available. + Details
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Balance Type: | debit
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- Definition Defined Contribution Plan Employer Matching Contribution Percent For First Compensation Slab + References No definition available. + Details
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- Definition Defined Contribution Plan Employer Matching Contribution Percent For Next Compensation Slab + References No definition available. + Details
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- Definition Participant Contribution On Pre Tax Basis Under Retirement Plan + References No definition available. + Details
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- Definition Percentage Of Employees Eligible Compensation That Represents Maximum Amount Of Employer Matching Contributions To Four Zero One K Plan + References No definition available. + Details
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- Definition Percentage Of Employers Contribution Based On Participants Compensation + References No definition available. + Details
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- Definition Retirement Plan Expense + References No definition available. + Details
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Balance Type: | debit
Period Type: | duration

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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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- Definition Maximum percentage of employee gross pay, by the terms of the plan, that the employer may contribute to a defined contribution plan. + References No definition available. + Details
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