Amount and Nature of Net Assets Restricted from Payment of Dividends (Parenthetical) (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Restricted Assets [Line Items]
Cash held in trust	$ 4,000,000
Insurance Companies | Fixed maturities
Restricted Assets [Line Items]
Restricted net assets,amortized cost	9,607,000	10,163,000
Lloyd's Operations | Fixed maturities
Restricted Assets [Line Items]
Restricted net assets,amortized cost	$ 419,271,000	$ 386,275,000