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Segment Information (Reconciliation of Segment Results to Income from Continuing Operations, before Federal Income Tax) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total investment revenues	$ 344,188	$ 222,890	$ 236,965
Interest expense	(29,165)	(30,839)	(33,668)
Corporate expenses	(28,305)	(25,412)	(30,900)
Income before federal income tax	505,310	302,988	336,390
Preferred Stock Dividends, Income Statement Impact	(9,353)	0	0
Income available to common stockholders, before tax	495,957	302,988	336,390
Standard Commercial Lines [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	198,596	151,731	145,990
Standard Personal Lines
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	3,966	(15,508)	8,260
E&S Lines [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	16,030	126	9,743
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total all segments	$ 562,780	$ 359,239	$ 400,958

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