Concentration of Operations - Net Premiums Earned for the Different Lines of Business (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned	$ 92,097	$ 89,918	$ 90,728	$ 95,961	$ 95,034	$ 90,504	$ 95,569	$ 94,787	$ 368,704	$ 375,894	$ 375,747
Premium earned percentage									100.00%	100.00%	100.00%
Workers Compensation [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned									$ 368,704	$ 375,894	$ 375,746
Premium earned percentage									100.00%	100.00%	100.00%
General Liability [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Net premiums earned											$ 1
Premium earned percentage									0.00%	0.00%	0.00%