Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		$ 4,494,591	$ 4,134,797
Unrealized Gains		102,250	133,303
Unrealized Losses		(23,844)	(10,578)
Total AFS securities		4,572,997	4,257,522
AFS Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		4,273,771	3,975,786
Unrealized Gains		88,662	100,578
Unrealized Losses		(11,387)	(10,242)
Total AFS securities		4,351,046	4,066,122
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		109,062	116,666
Unrealized Gains		6,069	7,592
Unrealized Losses		(1)	(128)
Total AFS securities		115,130	124,130
AFS Fixed Income Securities [Member] | Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		19,030	27,035
Unrealized Gains		657	796
Unrealized Losses		0	0
Total AFS securities		19,687	27,831
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		1,303,188	1,208,776
Unrealized Gains		35,552	38,217
Unrealized Losses		(545)	(729)
Total AFS securities		1,338,195	1,246,264
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		1,859,834	1,763,427
Unrealized Gains		35,222	42,188
Unrealized Losses		(8,882)	(5,809)
Total AFS securities		1,886,174	1,799,806
AFS Fixed Income Securities [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		255,716	176,837
Unrealized Gains		1,312	760
Unrealized Losses		(105)	(373)
Total AFS securities		256,923	177,224
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	[1]	220,009	177,932
Unrealized Gains	[1]	2,450	2,438
Unrealized Losses	[1]	(457)	(777)
Total AFS securities	[1]	222,002	179,593
Government guaranteed agency securities fair value		7,400	13,200
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	[2]	506,932	505,113
Unrealized Gains	[2]	7,400	8,587
Unrealized Losses	[2]	(1,397)	(2,426)
Total AFS securities	[2]	512,935	511,274
Government guaranteed agency securities fair value		22,500	32,400
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		220,820	159,011
Unrealized Gains		13,588	32,725
Unrealized Losses		(12,457)	(336)
Total AFS securities		221,951	191,400
Equity Securities [Member] | Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		208,995	159,011
Unrealized Gains		13,542	32,725
Unrealized Losses		(12,340)	(336)
Total AFS securities		210,197	$ 191,400
Equity Securities [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		11,825
Unrealized Gains		46
Unrealized Losses		(117)
Total AFS securities		$ 11,754

[1] CMBS includes government guaranteed agency securities with a fair value of $7.4 million at September 30, 2015 and $13.2 million at December 31, 2014.

[2] RMBS includes government guaranteed agency securities with a fair value of $22.5 million at September 30, 2015 and $32.4 million at December 31, 2014.