Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) location	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) segment location	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | segment			2
Net premiums earned	$ 260,069	$ 239,421	$ 754,854	$ 681,817
Investment income, net of investment expenses	26,690	24,050	73,421	74,205
Net realized investment gains	2,590	966	6,241	2,622
Other income	145	123	436	318
Total revenues	289,494	264,560	834,952	758,962
Net income	12,368	19,534	37,909	58,231
Assets	4,107,037	3,876,016	4,107,037	3,876,016	$ 3,890,376
Invested assets	$ 3,253,149	3,096,454	$ 3,253,149	3,096,454	$ 3,142,760
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Number of domestic locations | location	7		7
Total revenues	$ 255,625	230,441	$ 731,825	662,294
Net income	11,628	18,020	37,083	54,420
Assets	2,468,258	2,231,851	2,468,258	2,231,851
Invested assets	1,735,153	1,572,222	1,735,153	1,572,222
Life Insurance
Segment Reporting Information [Line Items]
Total revenues	33,869	34,119	103,127	96,668
Net income	740	1,514	826	3,811
Assets	1,638,779	1,644,165	1,638,779	1,644,165
Invested assets	1,517,996	1,524,232	1,517,996	1,524,232
Operating Segments
Segment Reporting Information [Line Items]
Net premiums earned	260,069	239,620	754,854	682,405
Investment income, net of investment expenses	26,728	24,075	73,533	74,233
Net realized investment gains	2,590	966	6,241	2,622
Other income	145	123	436	318
Total revenues	289,532	264,784	835,064	759,578
Operating Segments | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net premiums earned	239,469	218,993	691,976	628,396
Investment income, net of investment expenses	14,065	10,741	35,129	33,610
Net realized investment gains	2,129	732	4,832	316
Other income	0	0	0	0
Total revenues	255,663	230,466	731,937	662,322
Operating Segments | Life Insurance
Segment Reporting Information [Line Items]
Net premiums earned	20,600	20,627	62,878	54,009
Investment income, net of investment expenses	12,663	13,334	38,404	40,623
Net realized investment gains	461	234	1,409	2,306
Other income	145	123	436	318
Total revenues	33,869	34,318	103,127	97,256
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues	(38)	(224)	(112)	(616)
Intersegment Eliminations | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total revenues	(38)	(25)	(112)	(28)
Intersegment Eliminations | Life Insurance
Segment Reporting Information [Line Items]
Total revenues	$ 0	$ (199)	$ 0	$ (588)