Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Year	Dec. 31, 2010	Dec. 31, 2011 Equity Securities Maximum	Dec. 31, 2011 Lloyd's Operations	Dec. 31, 2010 Lloyd's Operations	Dec. 31, 2011 Lloyd's Operations Syndicate 1221	Dec. 31, 2010 Lloyd's Operations Syndicate 1221	Dec. 31, 2009 Lloyd's Operations Syndicate 1221	Dec. 31, 2011 Navigators Insurance Company	Dec. 31, 2011 Underwriting agencies	Dec. 31, 2010 Underwriting agencies
Goodwill and Intangible Assets Disclosure [Line Items]
Percentage of Navigators Specialty Insurance Company reinsured by Navigators Insurance Company									100.00%
Percentage control of stamp capacity						100.00%	100.00%	100.00%
Percentage of fair value over cost			80.00%
Property, Plant and Equipment, Useful Life, Minimum	3
Property, Plant and Equipment, Useful Life, Maximum	7
Goodwill and other intangible assets	$ 6,869,000	$ 6,925,000		$ 4,300,000	$ 4,400,000					$ 2,500,000	$ 2,500,000
Goodwill	4,800,000	4,800,000
Other intangible assets	$ 2,100,000	$ 2,100,000