Segment Information - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 Segment	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Number of business segments									2
Combined ratio indicating underwriting profit									100.00%
Combined ratio indicating underwriting loss									100.00%
Net earned premiums	$ 219,902	$ 213,895	$ 205,814	$ 202,328	$ 201,566	$ 201,262	$ 196,017	$ 183,119	$ 841,939	$ 781,964	$ 691,645
Navigators Insurance Company
Segment Reporting Information [Line Items]
Percentage of Navigators Specialty Insurance Company reinsured by Navigators Insurance Company	100.00%								100.00%
Insurance
Segment Reporting Information [Line Items]
Net earned premiums									639,338	571,439	472,463
Insurance | UK Branch
Segment Reporting Information [Line Items]
Net earned premiums									$ 44,600	$ 63,900	$ 88,300