Income Taxes [Line Items]

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- Definition

Non-U.S. insurance income constituting taxable income under Sub Part F of the IRC.

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- Definition

Statutory rate on the foreign source insurance income and foreign tax credit.

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- Definition

Tax Credit Carryforward, Expiration Year

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- Definition

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from state taxes.

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- Definition

Amount of deferred tax liability attributable to taxable temporary differences from undistributed earnings of subsidiaries and other recognized entities not within the country of domicile of the entity.

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- Definition

Amount of undistributed earnings of foreign subsidiaries intended to be permanently reinvested outside the country of domicile.

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- Definition

Amount of unrecognized tax benefits.

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Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Undistributed earnings of non-U.S. subsidiaries	$ 156,600,000
Taxes payable on undistributed earnings	2,700,000
Unrecognized tax benefits	0	$ 0	$ 0
Interest or penalties related to unrecognized tax benefits	0	0	$ 0
Deferred Tax Assets: State and Local	$ 699,000	$ 721,000
United Kingdom
Income Taxes [Line Items]
Foreign effective income tax rate	35.00%
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%
State and Local Jurisdiction \| Maximum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2034
State and Local Jurisdiction \| Minimum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2026