Concentration of Operations - Net Premiums Earned for the Different Lines of Business (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned	$ 95,034	$ 90,504	$ 95,569	$ 94,787	$ 97,070	$ 95,928	$ 93,516	$ 89,233	$ 375,894	$ 375,747	$ 329,983
Premium earned percentage									100.00%	100.00%	100.00%
Workers Compensation [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 375,894	$ 375,746	$ 329,986
Premium earned percentage									100.00%	100.00%	100.00%
General Liability [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned										$ 1	$ (3)
Premium earned percentage									0.00%	0.00%	0.00%