Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Undistributed earnings of non-U.S. subsidiaries	$ 60,900,000
Taxes payable on undistributed earnings	1,200,000
Deferred Tax Assets: State and Local	242,000	2,185,000
State and local net operating loss carry-forwards	$ 200,000	$ 1,400,000
United Kingdom
Income Taxes [Line Items]
Foreign effective income tax rate	35.00%
Corporate tax rate	28.00%
United Kingdom \| Syndicate 1221 \| Maximum
Income Taxes [Line Items]
Percentage of premiums	50.00%
United Kingdom \| Syndicate 1221 \| Minimum
Income Taxes [Line Items]
Foreign effective income tax rate	35.00%
United Kingdom \| Expected Future Tax Rate
Income Taxes [Line Items]
Corporate tax rate	26.00%
State and Local Jurisdiction \| Maximum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2030
State and Local Jurisdiction \| Minimum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2024

The tax effect as of the balance sheet date of the amount of excess of tax deductions over gross income in a year which cannot be used on the tax return of a state or local jurisdiction 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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The amount as of the balance sheet date of the estimated future tax effects attributable to undistributed earnings of subsidiaries and other recognized entities in countries outside the country of domicile which will increase future taxable income when such earnings are distributed into the country of domicile.

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