Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015 segment	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Number of business segments	2us-gaap_NumberOfOperatingSegments
Net premiums earned	$ 213,171us-gaap_PremiumsEarnedNet	$ 193,341us-gaap_PremiumsEarnedNet
Investment income, net of investment expenses	24,363us-gaap_NetInvestmentIncome	26,762us-gaap_NetInvestmentIncome
Net realized investment gains (losses)	887us-gaap_RealizedInvestmentGainsLosses	2,194us-gaap_RealizedInvestmentGainsLosses
Other income	63us-gaap_OtherIncome	607us-gaap_OtherIncome
Total revenues	238,484us-gaap_Revenues	222,904us-gaap_Revenues
Net income	23,679us-gaap_NetIncomeLoss	13,331us-gaap_NetIncomeLoss
Assets	3,864,251us-gaap_Assets	3,769,249us-gaap_Assets	3,856,689us-gaap_Assets
Invested assets	3,139,578us-gaap_Investments	3,115,734us-gaap_Investments	3,170,961us-gaap_Investments
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Number of business locations	7
Total revenues	210,645	192,504
Net income	23,103	11,811
Assets	2,166,432	2,032,501
Invested assets	1,562,710	1,486,783
Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	27,839	30,400
Net income	576	1,520
Assets	1,697,819	1,736,748
Invested assets	1,576,868	1,628,951
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net premiums earned	213,365	193,474
Investment income, net of investment expenses	24,346	26,712
Net realized investment gains (losses)	887	2,194
Other income	63	607
Total revenues	238,661	222,987
Operating Segments [Member] \| Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	200,137	179,494
Investment income, net of investment expenses	10,730	11,113
Net realized investment gains (losses)	(239)	1,367
Other income	0	480
Total revenues	210,628	192,454
Operating Segments [Member] \| Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	13,228	13,980
Investment income, net of investment expenses	13,616	15,599
Net realized investment gains (losses)	1,126	827
Other income	63	127
Total revenues	28,033	30,533
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Total revenues	(177)	(83)
Intersegment Elimination [Member] \| Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	17	50
Intersegment Elimination [Member] \| Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (194)	$ (133)

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