Reportable Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Direct and assumed premium written									$ 369,476	$ 341,286	$ 334,526
Net premiums earned	65,422	64,448	61,775	61,098	61,402	54,853	59,655	61,551	252,743	237,461	244,570
Underwriting gain (loss)									37,836	44,058	(25,467)
Reconciliation from Segment Totals to Consolidated [Abstract]
Underwriting gain (loss)									37,836	44,058	(25,467)
Net investment income									8,770	9,930	10,729
Net realized gains (losses) on investments									23,515	9,011	(17,803)
Corporate expenses									(15,211)	(16,393)	(12,748)
Income (loss) before federal income taxes									54,910	46,606	(45,289)
Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Direct and assumed premium written									314,784	284,200	274,101
Net premiums earned									202,785	186,586	186,422
Underwriting gain (loss)									25,558	23,491	19,646
Reconciliation from Segment Totals to Consolidated [Abstract]
Underwriting gain (loss)									25,558	23,491	19,646
Reinsurance [Member]
Segment Reporting Information [Line Items]
Direct and assumed premium written									54,692	57,086	60,425
Net premiums earned									49,958	50,875	58,148
Underwriting gain (loss)									12,278	20,567	(45,113)
Reconciliation from Segment Totals to Consolidated [Abstract]
Underwriting gain (loss)									$ 12,278	$ 20,567	$ (45,113)