Business Segments (Financial Information of Company Operating Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Earned Premiums	$ 1,568,703	$ 1,559,793	$ 3,138,744	$ 3,087,128
Investment Income and Funds	135,264	129,049	284,123	259,182
Other	144,082	167,072	295,600	316,815
Total revenues	1,848,049	1,855,914	3,718,467	3,663,125
Pre-Tax Income (Loss)	160,961	158,314	345,258	332,990
Net Income (Loss) to Common Stockholders	109,004	108,967	232,451	228,477
Net investment gains	40,453	6,315	92,801	13,658
Net investment gains, net of tax	26,294	4,105	60,321	8,878
Corporate, other and eliminations
Segment Reporting Information [Line Items]
Earned Premiums	0	0	0	0
Investment Income and Funds	11,054	9,522	23,226	16,025
Other	80,645	133,154	161,528	248,761
Total revenues	91,699	142,676	184,754	264,786
Pre-Tax Income (Loss)	(80,397)	(48,335)	(153,034)	(108,714)
Net Income (Loss) to Common Stockholders	(52,056)	(30,954)	(99,311)	(70,110)
Insurance
Segment Reporting Information [Line Items]
Earned Premiums	1,415,586	1,390,744	2,828,755	2,757,350
Insurance | Operating Segments
Segment Reporting Information [Line Items]
Earned Premiums	1,415,586	1,390,744	2,828,755	2,757,350
Investment Income and Funds	102,719	94,155	214,628	193,605
Other	22,984	27,603	41,271	54,396
Total revenues	1,541,289	1,512,502	3,084,654	3,005,351
Pre-Tax Income (Loss)	186,134	176,500	386,127	376,153
Net Income (Loss) to Common Stockholders	124,442	119,135	257,458	253,639
Reinsurance
Segment Reporting Information [Line Items]
Earned Premiums	153,117	169,049	309,989	329,778
Reinsurance | Operating Segments
Segment Reporting Information [Line Items]
Earned Premiums	153,117	169,049	309,989	329,778
Investment Income and Funds	21,491	25,372	46,269	49,552
Other	0	0	0	0
Total revenues	174,608	194,421	356,258	379,330
Pre-Tax Income (Loss)	14,771	23,834	19,364	51,893
Net Income (Loss) to Common Stockholders	10,324	16,681	13,983	36,070
Re-insurance - International | Operating Segments
Segment Reporting Information [Line Items]
Total revenues	50,000	50,000	101,000	105,000
Net investment gains
Segment Reporting Information [Line Items]
Earned Premiums	0	0
Investment Income and Funds	0	0		0
Insurance-International Segment | Operating Segments
Segment Reporting Information [Line Items]
Total revenues	$ 168,000	$ 179,000	$ 347,000	$ 359,000