Reconciliation of Basic and Diluted Earnings per Share Computations (Parenthetical) (Detail)	Jan. 20, 2017	Dec. 06, 2016
Earnings Per Share Disclosure [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.
Subsequent Event [Member]
Earnings Per Share Disclosure [Line Items]
Stock split ratio	2
Stockholders equity, stock split	We completed a two-for-one stock split on January 20, 2017.