Organization and Summary of Significant Accounting Policies - Additional Information (Detail)	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Navigators Insurance Company
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of Navigators Specialty Insurance Company reinsured by Navigators Insurance Company	100.00%
Lloyd's | Syndicate 1221
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage control of stamp capacity	100.00%	100.00%	100.00%