Summary of Changes In Carrying Amount of Goodwill By Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Acquired Intangible Assets [Line Items]
Beginning balance	$ 6,521	$ 4,820
Acquisition of American Reliable on January 1, 2015	0	1,701
Ending balance	6,521	6,521
Commercial Lines Segment
Acquired Intangible Assets [Line Items]
Beginning balance	4,820	4,820
Ending balance	4,820	4,820
Personal Lines Segment
Acquired Intangible Assets [Line Items]
Beginning balance	1,701
Acquisition of American Reliable on January 1, 2015		1,701
Ending balance	$ 1,701	$ 1,701