Securities In An Unrealized Loss Position Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 3,030,389	$ 2,024,847
Gross Unrealized Losses, Less than 12 Months	52,287	20,681
Fair Value, 12 Months or Greater	625,695	870,357
Gross Unrealized Losses, 12 Months or Greater	43,248	48,461
Fair Value, Total	3,656,084	2,895,204
Gross Unrealized Losses, Total	95,535	69,142
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	72,300	84,750
Gross Unrealized Losses, Less than 12 Months	1,656	522
Fair Value, 12 Months or Greater	73,593	84,850
Gross Unrealized Losses, 12 Months or Greater	1,899	2,635
Fair Value, Total	145,893	169,600
Gross Unrealized Losses, Total	3,555	3,157
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	873,578	158,594
Gross Unrealized Losses, Less than 12 Months	12,783	631
Fair Value, 12 Months or Greater	108,782	150,284
Gross Unrealized Losses, 12 Months or Greater	3,278	3,389
Fair Value, Total	982,360	308,878
Gross Unrealized Losses, Total	16,061	4,020
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	222,473	75,739
Gross Unrealized Losses, Less than 12 Months	2,903	332
Fair Value, 12 Months or Greater	212,426	312,922
Gross Unrealized Losses, 12 Months or Greater	7,704	9,169
Fair Value, Total	434,899	388,661
Gross Unrealized Losses, Total	10,607	9,501
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	1,669,868	1,586,238
Gross Unrealized Losses, Less than 12 Months	18,973	8,697
Fair Value, 12 Months or Greater	159,708	214,628
Gross Unrealized Losses, 12 Months or Greater	14,455	16,084
Fair Value, Total	1,829,576	1,800,866
Gross Unrealized Losses, Total	33,428	24,781
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	131,227	76,471
Gross Unrealized Losses, Less than 12 Months	4,036	3,907
Fair Value, 12 Months or Greater	48,528	85,025
Gross Unrealized Losses, 12 Months or Greater	12,896	14,158
Fair Value, Total	179,755	161,496
Gross Unrealized Losses, Total	16,932	18,065
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	2,969,446	1,981,792
Gross Unrealized Losses, Less than 12 Months	40,351	14,089
Fair Value, 12 Months or Greater	603,037	847,709
Gross Unrealized Losses, 12 Months or Greater	40,232	45,435
Fair Value, Total	3,572,483	2,829,501
Gross Unrealized Losses, Total	80,583	59,524
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	13,584	27,126
Gross Unrealized Losses, Less than 12 Months	1,267	1,139
Fair Value, 12 Months or Greater	22,658	22,648
Gross Unrealized Losses, 12 Months or Greater	3,016	3,026
Fair Value, Total	36,242	49,774
Gross Unrealized Losses, Total	4,283	4,165
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	60,943	43,055
Gross Unrealized Losses, Less than 12 Months	11,936	6,592
Fair Value, 12 Months or Greater	22,658	22,648
Gross Unrealized Losses, 12 Months or Greater	3,016	3,026
Fair Value, Total	83,601	65,703
Gross Unrealized Losses, Total	14,952	9,618
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	47,359	15,929
Gross Unrealized Losses, Less than 12 Months	10,669	5,453
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	47,359	15,929
Gross Unrealized Losses, Total	10,669	$ 5,453
Noninvestment Grade Investments at Loss Less than 5 Million [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	114,366
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	24,150
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	$ 90,216