Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 segments	Mar. 31, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of business segments	2
Net premiums earned	$ 176,817	$ 161,503
Investment income, net of investment expenses	26,464	29,146
Net realized investment gains	1,909	2,794
Other income	115	256
Total revenues	205,305	193,699
Net income	22,393	19,184
Assets	3,724,690	3,687,175	3,694,653
Invested assets	3,063,359	3,022,184	3,044,363
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Number of business locations	6
Total revenues	174,227	158,674
Net income	20,730	16,636
Assets	1,941,227	1,901,748
Invested assets	1,378,188	1,325,793
Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	31,078	35,025
Net income	1,663	2,548
Assets	1,783,463	1,785,427
Invested assets	1,685,171	1,696,391
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net premiums earned	176,940	161,614
Investment income, net of investment expenses	26,400	29,186
Net realized investment gains	1,909	2,747
Other income	115	256
Total revenues	205,364	193,803
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	162,701	146,756
Investment income, net of investment expenses	10,421	10,678
Net realized investment gains	1,029	1,133
Other income	12	100
Total revenues	174,163	158,667
Operating Segments [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	14,239	14,858
Investment income, net of investment expenses	15,979	18,508
Net realized investment gains	880	1,614
Other income	103	156
Total revenues	31,201	35,136
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Total revenues	(59)	(104)
Intersegment Elimination [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	64	7
Intersegment Elimination [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (123)	$ (111)