Securities In An Unrealized Loss Position Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 1,245,707	$ 3,497,447
Gross Unrealized Losses, Less than 12 Months	18,751	78,466
Fair Value, 12 Months or Greater	869,118	672,929
Gross Unrealized Losses, 12 Months or Greater	28,956	35,482
Fair Value, Total	2,114,825	4,170,376
Gross Unrealized Losses, Total	47,707	113,948
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	7,993	101,660
Gross Unrealized Losses, Less than 12 Months	50	487
Fair Value, 12 Months or Greater	41,081	64,500
Gross Unrealized Losses, 12 Months or Greater	632	1,846
Fair Value, Total	49,074	166,160
Gross Unrealized Losses, Total	682	2,333
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	57,499	501,952
Gross Unrealized Losses, Less than 12 Months	667	4,404
Fair Value, 12 Months or Greater	132,435	106,681
Gross Unrealized Losses, 12 Months or Greater	1,903	1,865
Fair Value, Total	189,934	608,633
Gross Unrealized Losses, Total	2,570	6,269
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	170,852	381,986
Gross Unrealized Losses, Less than 12 Months	1,871	3,639
Fair Value, 12 Months or Greater	110,882	184,807
Gross Unrealized Losses, 12 Months or Greater	2,529	7,669
Fair Value, Total	281,734	566,793
Gross Unrealized Losses, Total	4,400	11,308
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	866,041	1,091,078
Gross Unrealized Losses, Less than 12 Months	7,972	7,703
Fair Value, 12 Months or Greater	322,613	190,467
Gross Unrealized Losses, 12 Months or Greater	8,364	6,711
Fair Value, Total	1,188,654	1,281,545
Gross Unrealized Losses, Total	16,336	14,414
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	84,791	1,232,940
Gross Unrealized Losses, Less than 12 Months	4,208	35,406
Fair Value, 12 Months or Greater	207,097	76,797
Gross Unrealized Losses, 12 Months or Greater	11,133	8,987
Fair Value, Total	291,888	1,309,737
Gross Unrealized Losses, Total	15,341	44,393
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	35,055	169,190
Gross Unrealized Losses, Less than 12 Months	2,346	8,822
Fair Value, 12 Months or Greater	22,116	19,528
Gross Unrealized Losses, 12 Months or Greater	1,837	3,867
Fair Value, Total	57,171	188,718
Gross Unrealized Losses, Total	4,183	12,689
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	1,222,231	3,478,806
Gross Unrealized Losses, Less than 12 Months	17,114	60,461
Fair Value, 12 Months or Greater	836,224	642,780
Gross Unrealized Losses, 12 Months or Greater	26,398	30,945
Fair Value, Total	2,058,455	4,121,586
Gross Unrealized Losses, Total	43,512	91,406
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	5,793	0
Gross Unrealized Losses, Less than 12 Months	788	0
Fair Value, 12 Months or Greater	24,681	22,320
Gross Unrealized Losses, 12 Months or Greater	992	3,353
Fair Value, Total	30,474	22,320
Gross Unrealized Losses, Total	1,780	3,353
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	23,476	18,641
Gross Unrealized Losses, Less than 12 Months	1,637	18,005
Fair Value, 12 Months or Greater	32,894	30,149
Gross Unrealized Losses, 12 Months or Greater	2,558	4,537
Fair Value, Total	56,370	48,790
Gross Unrealized Losses, Total	4,195	22,542
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	17,683	18,641
Gross Unrealized Losses, Less than 12 Months	849	18,005
Fair Value, 12 Months or Greater	8,213	7,829
Gross Unrealized Losses, 12 Months or Greater	1,566	1,184
Fair Value, Total	25,896	26,470
Gross Unrealized Losses, Total	2,415	$ 19,189
Noninvestment Grade Investments at Loss Less than 5 Million [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	140,819
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	23,910
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	$ 74,180