Summary of Business Segment Information (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Specialty Property
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations		$ 64		$ 298
Commercial Specialty
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations		77		367
Farm, Ranch & Stable
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations		$ 28		$ 137
American Reliable Insurance Company | Specialty Property
Segment Reporting Information [Line Items]
Quota share agreement percentage	100.00%	100.00%	100.00%	100.00%
Ceded premiums written	$ (23)	$ (3)	$ (200)	$ (1,859)