Schedule VI. Supplemental Information Concerning Property-Casualty Insurance Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Deferred Policy Acquisition Cost	$ 20,412	$ 19,649	$ 19,171
Reserves for Unpaid Loss and Loss Adjustment Expense	718,033	687,602	614,557
Unearned Premium	167,983	168,576	164,296
Earned Premium	375,894	375,747	329,983
Net Investment Income	27,902	27,214	27,029
Loss and LAE Related to Current Period	262,387	268,633	241,584
Loss and LAE Related to Prior Periods	(47,814)	(23,717)	(12,611)
Amortization of Deferred Policy Acquisition Costs	(44,841)	(43,817)	(40,526)
Paid Claims and Claim Adjustment Expenses	189,666	182,506	178,375
Net Premiums Written	$ 375,301	$ 380,026	$ 353,752