Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 40,720	$ 39,343	$ 37,792
Loss and settlement expense reserves	678,774	661,309	610,181
Unearned premiums	239,435	232,093	220,627
Premium revenue	570,266	540,722	515,506
Net investment income	45,582	46,465	43,022
Losses and settlement expenses incurred	370,736	385,474	333,287
Amortization of deferred policy acquisition costs	102,184	99,042	94,728
Other underwriting expenses	68,418	56,826	65,754
Premiums written	578,938	552,610	534,077
Property and casualty insurance [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	35,219	33,855	32,740
Loss and settlement expense reserves	480,413	463,458	425,758
Unearned premiums	212,652	204,357	191,714
Premium revenue	447,197	422,381	392,719
Net investment income	32,668	33,509	31,397
Losses and settlement expenses incurred	291,883	298,033	260,917
Amortization of deferred policy acquisition costs	75,701	72,768	68,851
Other underwriting expenses	63,954	54,385	62,522
Premiums written	454,434	433,707	405,049
Reinsurance [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	5,501	5,488	5,052
Loss and settlement expense reserves	198,361	197,851	184,423
Unearned premiums	26,783	27,736	28,913
Premium revenue	123,069	118,341	122,787
Net investment income	12,923	12,968	11,635
Losses and settlement expenses incurred	78,853	87,441	72,370
Amortization of deferred policy acquisition costs	26,483	26,274	25,877
Other underwriting expenses	4,464	2,441	3,232
Premiums written	124,504	118,903	129,028
Parent company [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	0	0	0
Loss and settlement expense reserves	0	0	0
Unearned premiums	0	0	0
Premium revenue	0	0	0
Net investment income	(9)	(12)	(10)
Losses and settlement expenses incurred	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Other underwriting expenses	0	0	0
Premiums written	$ 0	$ 0	$ 0