Amount and Nature of Net Assets Restricted from Payment of Dividends (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	$ 523,425		$ 520,886
Insurance Companies
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	13,234	[1]	12,605	[1]
Insurance Companies | Fixed maturities
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	11,732		11,105
Insurance Companies | Short-term investments
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	290		290
Insurance Companies | Cash
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	1,212		1,210
Lloyd's
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	510,191	[2]	508,281	[2]
Lloyd's | Fixed maturities
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	447,679		398,808
Lloyd's | Short-term investments
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	61,549		108,485
Lloyd's | Cash
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Total Restricted Net Assets	$ 963		$ 988

[1] The restricted net assets for the Insurance Companies primarily consist of fixed maturities on deposit with various state insurance departments. The cash as of December 31, 2014 and 2013, as presented in the table above, was on deposit with a U.K. bank to comply with the regulatory requirements of the Prudential Regulation Authority for the underwriting activities of the U.K. Branch.

[2] The restricted net assets for the Lloyd's Operations consists of fixed maturities and cash held in trust for the benefit of syndicate policyholders and short term investments primarily consisting of overseas deposits in various countries with Lloyd's to support underwriting activities in those countries.