Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net premiums earned	$ 65,995	$ 65,445	$ 65,449	$ 66,446	$ 68,933	$ 65,947	$ 62,905	$ 63,842	$ 263,335	$ 261,627	$ 252,743
Reconciliation from Segment Totals to Consolidated [Abstract]
Net investment income									12,498	9,055	8,770
Income before federal income taxes									33,952	44,398	54,910
Reportable Segments [Member]
Segment Reporting Information [Line Items]
Direct and assumed premium written									383,553	382,388	369,476
Net premiums earned									263,335	261,627	252,743
Underwriting gain									38,927	34,810	37,836
Reconciliation from Segment Totals to Consolidated [Abstract]
Underwriting gain									38,927	34,810	37,836
Reportable Segments [Member] | Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Direct and assumed premium written									366,668	343,200	314,784
Net premiums earned									242,364	224,683	202,785
Underwriting gain									40,431	32,663	25,558
Reconciliation from Segment Totals to Consolidated [Abstract]
Underwriting gain									40,431	32,663	25,558
Reportable Segments [Member] | Reinsurance [Member]
Segment Reporting Information [Line Items]
Direct and assumed premium written									16,885	39,188	54,692
Net premiums earned									20,971	36,944	49,958
Underwriting gain									(1,504)	2,147	12,278
Reconciliation from Segment Totals to Consolidated [Abstract]
Underwriting gain									(1,504)	2,147	12,278
Segment Reconciling Items [Member]
Reconciliation from Segment Totals to Consolidated [Abstract]
Net investment income									12,498	9,055	8,770
Net realized gains (losses) on investments									(1,261)	14,930	23,515
Corporate expenses									$ (16,212)	$ (14,397)	$ (15,211)