Dividends and Statutory Financial Information - Additional Information (Detail)	0 Months Ended				12 Months Ended			12 Months Ended
	Nov. 30, 2013 USD ($)	Nov. 30, 2013 GBP (£)	Dec. 31, 2013 USD ($)	Dec. 31, 2013 GBP (£)	Dec. 31, 2012 Navigators Insurance Company USD ($)	Dec. 31, 2011 Navigators Insurance Company USD ($)	Dec. 31, 2013 Navigators Insurance Company USD ($)	Dec. 31, 2013 Insurance USD ($)	Dec. 31, 2012 Insurance USD ($)	Dec. 21, 2011 Insurance USD ($)	Dec. 31, 2013 Insurance Minimum	Dec. 31, 2013 Insurance Maximum	Dec. 31, 2013 Lloyd's USD ($)	Dec. 31, 2012 Lloyd's USD ($)	Dec. 31, 2011 Lloyd's USD ($)	Dec. 31, 2013 Lloyd's GBP (£)	Dec. 31, 2012 Lloyd's GBP (£)	Dec. 31, 2013 Lloyd's Syndicate 1221 USD ($)	Dec. 31, 2013 Lloyd's Syndicate 1221 GBP (£)	Dec. 31, 2012 Lloyd's Syndicate 1221 USD ($)	Dec. 31, 2012 Lloyd's Syndicate 1221 GBP (£)	Dec. 31, 2011 Lloyd's Syndicate 1221
Statutory Accounting Practices [Line Items]
Maximum amount available for payment of dividends without prior regulatory approval							$ 80,400,000
Dividends paid to Parent Company					15,000,000	45,000,000
Statutory net income								59,400,000	28,600,000	16,300,000
Statutory capital and surplus								804,100,000	682,900,000				124,200,000	110,000,000		74,800,000	67,500,000
Risk based capital ratio					295.10%		304.20%
Insurance examinations period											3 years	5 years
FAL requirement set by Lloyd's for Syndicate 1221 based on its business plan, approved in November 2012 and 2011													279,300,000	223,400,000		168,300,000	137,100,000
Valuation of assets and letters of credit posted																		280,200,000	168,800,000	227,300,000	139,500,000
Pre-tax regulatory income													21,000,000	54,900,000	5,300,000
Percentage control of stamp capacity																		100.00%	100.00%	100.00%	100.00%	100.00%
Undistributed Profit	127,400,000	76,700,000
Dividend Capacity			$ 11,600,000	£ 7,000,000