Concentration of Operations - Net Premiums Earned for the Top Ten States (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned	$ 87,377	$ 85,118	$ 82,749	$ 90,912	$ 92,097	$ 89,918	$ 90,728	$ 95,961	$ 346,156	$ 368,704	$ 375,894
Premium earned percentage									100.00%	100.00%	100.00%
Georgia [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 40,801	$ 38,168	$ 40,497
Premium earned percentage									11.80%	10.40%	10.80%
Florida [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 34,615	$ 29,051	$ 24,792
Premium earned percentage									10.00%	7.90%	6.60%
Pennsylvania [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 32,931	$ 39,460	$ 36,294
Premium earned percentage									9.50%	10.70%	9.70%
Louisiana [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 25,422	$ 30,426	$ 38,874
Premium earned percentage									7.30%	8.30%	10.30%
Illinois [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 22,169	$ 25,796	$ 23,285
Premium earned percentage									6.40%	7.00%	6.20%
North Carolina [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 18,388	$ 20,784	$ 20,062
Premium earned percentage									5.30%	5.60%	5.30%
Virginia [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 16,298	$ 16,599	$ 15,656
Premium earned percentage									4.70%	4.50%	4.20%
Minnesota [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 13,968	$ 15,130	$ 14,618
Premium earned percentage									4.00%	4.10%	3.90%
Wisconsin [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 13,790	$ 13,544	$ 11,203
Premium earned percentage									4.00%	3.70%	3.00%
South Carolina [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 13,327	$ 13,897	$ 12,955
Premium earned percentage									3.90%	3.80%	3.40%
All Others [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 114,447	$ 125,849	$ 137,658
Premium earned percentage									33.10%	34.00%	36.60%