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, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 2,455,750	$ 3,085,977
Gross Unrealized Losses, Less than 12 Months	52,939	84,259
Fair Value, 12 Months or Greater	427,843	355,098
Gross Unrealized Losses, 12 Months or Greater	25,995	33,194
Fair Value, Total	2,883,593	3,441,075
Gross Unrealized Losses, Total	78,934	117,453
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	306,133	260,882
Gross Unrealized Losses, Less than 12 Months	8,835	7,927
Fair Value, 12 Months or Greater	4,300	2,163
Gross Unrealized Losses, 12 Months or Greater	342	55
Fair Value, Total	310,433	263,045
Gross Unrealized Losses, Total	9,177	7,982
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	415,060	899,613
Gross Unrealized Losses, Less than 12 Months	8,233	24,503
Fair Value, 12 Months or Greater	96,482	87,345
Gross Unrealized Losses, 12 Months or Greater	3,011	5,334
Fair Value, Total	511,542	986,958
Gross Unrealized Losses, Total	11,244	29,837
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	480,012	578,603
Gross Unrealized Losses, Less than 12 Months	11,824	17,964
Fair Value, 12 Months or Greater	161,965	140,648
Gross Unrealized Losses, 12 Months or Greater	7,679	8,965
Fair Value, Total	641,977	719,251
Gross Unrealized Losses, Total	19,503	26,929
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	964,728	1,013,373
Gross Unrealized Losses, Less than 12 Months	9,508	17,066
Fair Value, 12 Months or Greater	137,535	105,074
Gross Unrealized Losses, 12 Months or Greater	11,049	13,034
Fair Value, Total	1,102,263	1,118,447
Gross Unrealized Losses, Total	20,557	30,100
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	286,805	320,215
Gross Unrealized Losses, Less than 12 Months	14,507	16,286
Fair Value, 12 Months or Greater	5,220	0
Gross Unrealized Losses, 12 Months or Greater	581	0
Fair Value, Total	292,025	320,215
Gross Unrealized Losses, Total	15,088	16,286
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	2,452,738	3,072,686
Gross Unrealized Losses, Less than 12 Months	52,907	83,746
Fair Value, 12 Months or Greater	405,502	335,230
Gross Unrealized Losses, 12 Months or Greater	22,662	27,388
Fair Value, Total	2,858,240	3,407,916
Gross Unrealized Losses, Total	75,569	111,134
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	0	0
Gross Unrealized Losses, Less than 12 Months	0	0
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	0	0
Gross Unrealized Losses, Total	0	0
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	3,012	13,291
Gross Unrealized Losses, Less than 12 Months	32	513
Fair Value, 12 Months or Greater	22,341	19,868
Gross Unrealized Losses, 12 Months or Greater	3,333	5,806
Fair Value, Total	25,353	33,159
Gross Unrealized Losses, Total	3,365	6,319
Equity securities available for sale
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	3,012	13,291
Gross Unrealized Losses, Less than 12 Months	32	513
Fair Value, 12 Months or Greater	22,341	19,868
Gross Unrealized Losses, 12 Months or Greater	3,333	5,806
Fair Value, Total	25,353	33,159
Gross Unrealized Losses, Total	$ 3,365	$ 6,319