Securities In An Unrealized Loss Position Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 1,549,410	$ 2,024,847
Gross Unrealized Losses, Less than 12 Months	21,964	20,681
Fair Value, 12 Months or Greater	666,589	870,357
Gross Unrealized Losses, 12 Months or Greater	42,234	48,461
Fair Value, Total	2,215,999	2,895,204
Gross Unrealized Losses, Total	64,198	69,142
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	57,281	84,750
Gross Unrealized Losses, Less than 12 Months	340	522
Fair Value, 12 Months or Greater	71,103	84,850
Gross Unrealized Losses, 12 Months or Greater	1,489	2,635
Fair Value, Total	128,384	169,600
Gross Unrealized Losses, Total	1,829	3,157
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	310,510	158,594
Gross Unrealized Losses, Less than 12 Months	1,753	631
Fair Value, 12 Months or Greater	112,892	150,284
Gross Unrealized Losses, 12 Months or Greater	2,693	3,389
Fair Value, Total	423,402	308,878
Gross Unrealized Losses, Total	4,446	4,020
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	76,098	75,739
Gross Unrealized Losses, Less than 12 Months	219	332
Fair Value, 12 Months or Greater	225,870	312,922
Gross Unrealized Losses, 12 Months or Greater	6,534	9,169
Fair Value, Total	301,968	388,661
Gross Unrealized Losses, Total	6,753	9,501
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	1,013,347	1,586,238
Gross Unrealized Losses, Less than 12 Months	5,917	8,697
Fair Value, 12 Months or Greater	172,712	214,628
Gross Unrealized Losses, 12 Months or Greater	13,859	16,084
Fair Value, Total	1,186,059	1,800,866
Gross Unrealized Losses, Total	19,776	24,781
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	39,512	76,471
Gross Unrealized Losses, Less than 12 Months	3,518	3,907
Fair Value, 12 Months or Greater	61,375	85,025
Gross Unrealized Losses, 12 Months or Greater	14,623	14,158
Fair Value, Total	100,887	161,496
Gross Unrealized Losses, Total	18,141	18,065
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	1,496,748	1,981,792
Gross Unrealized Losses, Less than 12 Months	11,747	14,089
Fair Value, 12 Months or Greater	643,952	847,709
Gross Unrealized Losses, 12 Months or Greater	39,198	45,435
Fair Value, Total	2,140,700	2,829,501
Gross Unrealized Losses, Total	50,945	59,524
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	4,017	27,126
Gross Unrealized Losses, Less than 12 Months	834	1,139
Fair Value, 12 Months or Greater	22,637	22,648
Gross Unrealized Losses, 12 Months or Greater	3,036	3,026
Fair Value, Total	26,654	49,774
Gross Unrealized Losses, Total	3,870	4,165
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	52,662	43,055
Gross Unrealized Losses, Less than 12 Months	10,217	6,592
Fair Value, 12 Months or Greater	22,637	22,648
Gross Unrealized Losses, 12 Months or Greater	3,036	3,026
Fair Value, Total	75,299	65,703
Gross Unrealized Losses, Total	13,253	9,618
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	48,645	15,929
Gross Unrealized Losses, Less than 12 Months	9,383	5,453
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	48,645	15,929
Gross Unrealized Losses, Total	9,383	5,453
Noninvestment Grade Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Total	$ 75,300