Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 segments	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of business segments			2
Net premiums earned	$ 194,219	$ 176,531	$ 557,403	$ 508,124
Investment income, net of investment expenses	27,278	28,665	82,761	86,560
Net realized investment gains (losses)	1,190	1,300	7,250	4,658
Other income	337	85	634	584
Total revenues	223,024	206,581	648,048	599,926
Net income	11,725	8,730	49,614	42,630
Assets	3,723,697	3,737,810	3,723,697	3,737,810	3,694,653
Invested assets	3,037,677	3,069,066	3,037,677	3,069,066	3,044,363
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Number of business locations	6		6
Total revenues	191,205	173,478	551,879	497,253
Net income	10,282	7,616	44,207	37,607
Assets	1,977,120	1,923,407	1,977,120	1,923,407
Invested assets	1,401,982	1,334,278	1,401,982	1,334,278
Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	31,819	33,103	96,169	102,673
Net income	1,443	1,114	5,407	5,023
Assets	1,746,577	1,814,403	1,746,577	1,814,403
Invested assets	1,635,695	1,734,788	1,635,695	1,734,788
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net premiums earned	194,342	176,644	557,772	508,459
Investment income, net of investment expenses	27,266	28,707	82,676	86,684
Net realized investment gains (losses)	1,190	1,300	7,250	4,658
Other income	337	85	634	584
Total revenues	223,135	206,736	648,332	600,385
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	178,553	161,232	511,781	461,902
Investment income, net of investment expenses	11,679	11,093	34,379	33,533
Net realized investment gains (losses)	816	1,214	5,405	1,765
Other income	145	(19)	229	177
Total revenues	191,193	173,520	551,794	497,377
Operating Segments [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	15,789	15,412	45,991	46,557
Investment income, net of investment expenses	15,587	17,614	48,297	53,151
Net realized investment gains (losses)	374	86	1,845	2,893
Other income	192	104	405	407
Total revenues	31,942	33,216	96,538	103,008
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Total revenues	(111)	(155)	(284)	(459)
Intersegment Elimination [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	12	(42)	85	(124)
Intersegment Elimination [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (123)	$ (113)	$ (369)	$ (335)