Subsequent Events - Additional Information (Detail)	Feb. 16, 2017 $ / shares	Jan. 20, 2017	Jan. 01, 2017	Dec. 30, 2016 shares	Dec. 06, 2016
Subsequent Event [Line Items]
Stock split ratio					2
Stockholders equity, stock split					On December 6, 2016, our Board of Directors declared a two-for-one stock split of The Navigators Group, Inc. Common stock, to be effected in the form of a stock dividend.
Number of additional shares for every share held | shares				1
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock split ratio		2
Stockholders equity, stock split		We completed a two-for-one stock split on January 20, 2017.
Dividend declaration date	Feb. 16, 2017
Common stock dividend declared per share | $ / shares	$ 0.045
Dividend payable date	Mar. 24, 2017
Dividend payable record date	Mar. 03, 2017
Percentage of ownership interest sold			100.00%
Subsequent Event [Member] | North American Property Business
Subsequent Event [Line Items]
Reinsurance arrangement			100.00%