Schedule VI - Supplemental Information Concerning Property-Casualty Insurance Operations (Details) - 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 costs	$ 40,720	$ 39,343	$ 37,792
Reserves for losses and settlement expenses	678,774	661,309	610,181
Discount, if any, deducted from reserves	0	0	0
Unearned premiums	239,435	232,093	220,627
Earned premiums	570,266	540,722	515,506
Net investment income	45,591	46,477	43,032
Losses and settlement expenses incurred related to current year	405,850	406,266	346,072
Losses and settlement expenses incurred related to prior years	(35,114)	(20,792)	(12,785)
Amortization of deferred policy acquisition costs	102,184	99,042	94,728
Paid losses and settlement expenses	348,081	330,087	305,266
Premiums written	$ 578,938	$ 552,610	$ 534,077