Segment Information (Details) $ in Thousands	3 Months Ended
Mar. 31, 2017 USD ($) segment location	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of business segments \| segment	2
Net premiums earned	$ 253,872	$ 241,298
Investment income, net of investment expenses	25,035	22,224
Net realized investment gains	3,954	2,055
Other income	198	108
Total revenues	283,059	265,685
Net income	19,936	22,427
Assets	4,096,985	3,975,992	$ 4,054,758
Invested assets	$ 3,305,456	3,172,329	$ 3,265,660
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Number of domestic locations \| location	6
Total revenues	$ 251,278	231,334
Net income	18,584	22,020
Assets	2,497,181	2,344,686
Invested assets	1,819,221	1,675,088
Life Insurance
Segment Reporting Information [Line Items]
Total revenues	31,781	34,351
Net income	1,352	407
Assets	1,599,804	1,631,306
Invested assets	1,486,235	1,497,241
Operating Segments
Segment Reporting Information [Line Items]
Net premiums earned	253,872	241,298
Investment income, net of investment expenses	25,055	22,261
Net realized investment gains	3,954	2,055
Other income	198	108
Total revenues	283,079	265,722
Operating Segments \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net premiums earned	236,444	220,225
Investment income, net of investment expenses	12,605	9,409
Net realized investment gains	2,249	1,737
Other income	0	0
Total revenues	251,298	231,371
Operating Segments \| Life Insurance
Segment Reporting Information [Line Items]
Net premiums earned	17,428	21,073
Investment income, net of investment expenses	12,450	12,852
Net realized investment gains	1,705	318
Other income	198	108
Total revenues	31,781	34,351
Intersegment eliminations
Segment Reporting Information [Line Items]
Total revenues	(20)	(37)
Intersegment eliminations \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total revenues	(20)	(37)
Intersegment eliminations \| Life Insurance
Segment Reporting Information [Line Items]
Total revenues	$ 0	$ 0

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