Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Income Taxes [Line Items]
Undistributed earnings of non-U.S. subsidiaries	$ 21,400,000
Taxes payable on undistributed earnings	2,200,000
Income tax (benefit) expense	13,354,000	6,643,000
Effective income tax rate	32.30%	32.30%
Deferred Tax Assets: State and Local	400,000		600,000
State and local net operating loss carry-forwards	$ 100,000		$ 100,000
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%
United States
Income Taxes [Line Items]
U.S. tax rate	35.00%
State and Local Jurisdiction | Maximum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2032
State and Local Jurisdiction | Minimum
Income Taxes [Line Items]
State and local tax carry-forwards expiration year	2024