Concentration of Operations - Net Premiums Earned for the Different Lines of Business (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned	$ 86,695	$ 81,596	$ 81,983	$ 79,709	$ 78,741	$ 72,425	$ 69,733	$ 69,790	$ 329,983	$ 290,689	$ 251,015
Premium earned percentage									100.00%	100.00%	100.00%
Workers Compensation [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									329,986	290,538	249,966
Premium earned percentage									100.00%	99.90%	99.60%
General Liability [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ (3)	$ 151	$ 1,049
Premium earned percentage									0.00%	0.10%	0.40%