Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 segments	Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of business segments			2
Net premiums earned	$ 186,367	$ 170,090	$ 363,184	$ 331,593
Investment income, net of investment expenses	29,019	28,749	55,483	57,895
Net realized investment gains (losses)	4,151	564	6,060	3,358
Other income	182	243	297	499
Total revenues	219,719	199,646	425,024	393,345
Net income	15,496	14,716	37,889	33,900
Assets	3,700,749	3,741,263	3,700,749	3,741,263	3,694,653
Invested assets	3,023,303	3,030,720	3,023,303	3,030,720	3,044,363
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Number of business locations	6		6
Total revenues	186,447	165,101	360,674	323,775
Net income	13,195	13,355	33,924	29,991
Assets	1,951,033	1,947,895	1,951,033	1,947,895
Invested assets	1,379,947	1,323,303	1,379,947	1,323,303
Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	33,272	34,545	64,350	69,570
Net income	2,301	1,361	3,965	3,909
Assets	1,749,716	1,793,368	1,749,716	1,793,368
Invested assets	1,643,356	1,707,417	1,643,356	1,707,417
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net premiums earned	186,490	170,201	363,430	331,815
Investment income, net of investment expenses	29,010	28,791	55,410	57,977
Net realized investment gains (losses)	4,151	611	6,060	3,358
Other income	182	243	297	499
Total revenues	219,833	199,846	425,197	393,649
Operating Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	170,527	153,914	333,228	300,670
Investment income, net of investment expenses	12,279	11,762	22,700	22,440
Net realized investment gains (losses)	3,560	(582)	4,589	551
Other income	72	96	84	196
Total revenues	186,438	165,190	360,601	323,857
Operating Segments [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums earned	15,963	16,287	30,202	31,145
Investment income, net of investment expenses	16,731	17,029	32,710	35,537
Net realized investment gains (losses)	591	1,193	1,471	2,807
Other income	110	147	213	303
Total revenues	33,395	34,656	64,596	69,792
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Total revenues	(114)	(200)	(173)	(304)
Intersegment Elimination [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	9	(89)	73	(82)
Intersegment Elimination [Member] | Life Insurance [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (123)	$ (111)	$ (246)	$ (222)