Income Tax - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Income Taxes [Line Items]
Operating loss carry forwards	$ 0
Capital loss carry forwards	$ 0

The tax effect as of the balance sheet date of the amount of future tax deductions arising from capital losses in excess of statutory limitations in historical filings, and which can only be utilized if sufficient tax-basis income is generated in future periods and providing tax laws continue to allow such utilization.

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The sum of the tax effects as of the balance sheet date of the amount of excesses of tax deductions over gross income in a year which cannot be used on the tax returns in the current year but can be carried forward to reduce taxable income or income taxes payable in a future year, for which there must be sufficient tax-basis income to utilize a portion or all of the carryforward amount to realize the deferred tax asset.

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