Segment Information (Income Before Federal Income Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Total investment revenues	$ 32,369	$ 49,523	$ 106,979	$ 133,588
Tax on investment income	7,614	13,858	26,186	36,374
Total investment income after federal income tax	24,755	35,665	80,793	97,214
Standard Commercial Lines [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ 44,027	$ 27,771	$ 109,304	$ 39,844
GAAP combined ratio	88.70%	92.10%	90.30%	96.20%
Statutory combined ratio	88.40%	90.90%	89.40%	95.50%
Standard Personal Lines [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ 2,826	$ 8,037	$ (4,295)	$ 95
GAAP combined ratio	96.10%	89.20%	102.00%	100.00%
Statutory combined ratio	95.00%	88.90%	101.70%	99.90%
Excess And Surplus Operations [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ (2,022)	$ (1,371)	$ (5,033)	$ (433)
GAAP combined ratio	104.40%	103.80%	104.00%	100.40%
Statutory combined ratio	101.10%	102.90%	101.80%	100.30%