Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum	Dec. 31, 2012 Equity Securities Maximum	Dec. 31, 2012 Navigators Insurance Company	Dec. 31, 2012 Lloyd's Operations	Dec. 31, 2011 Lloyd's Operations	Dec. 31, 2012 Lloyd's Operations Syndicate 1221	Dec. 31, 2011 Lloyd's Operations Syndicate 1221	Dec. 31, 2010 Lloyd's Operations Syndicate 1221	Dec. 31, 2012 NMC Operations	Dec. 31, 2011 NMC Operations
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			3 years	7 years
Goodwill and other intangible assets	$ 7,093,000	$ 6,869,000
Goodwill							2,400,000	2,300,000				2,500,000	2,500,000
Other intangible assets							2,200,000	2,100,000
Decrease in capitalized acquisition costs resulting from adoption of ASU 2010-26	$ 4,200,000