Investments (Securities Held to Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 6,641,083	$ 6,510,320
Gross Unrealized Gains	374,085	281,623
Gross Unrealized Losses	(35,823)	(135,799)
Fair Value	6,979,345	6,656,144
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	144,086	2,306,154
Less than 12 Months, Unrealized Losses	(346)	(121,620)
12 Months or Greater, Fair Value	1,246,858	149,558
12 Months or Greater, Unrealized Losses	(35,477)	(14,179)
Total, Fair Value	1,390,944	2,455,712
Total, Unrealized Losses	(35,823)	(135,799)
U.S. Agencies [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	23,075	23,088
Gross Unrealized Gains	1,177	1,700
Gross Unrealized Losses	0	0
Fair Value	24,252	24,788
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Total, Unrealized Losses	0	0
U.S. Treasury [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,917	1,913
Gross Unrealized Gains	436	434
Gross Unrealized Losses	0	0
Fair Value	2,353	2,347
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Total, Unrealized Losses	0	0
States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	431,661	423,286
Gross Unrealized Gains	25,868	13,433
Gross Unrealized Losses	(2,165)	(10,944)
Fair Value	455,364	425,775
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	128,711
Less than 12 Months, Unrealized Losses	0	(9,249)
12 Months or Greater, Fair Value	49,578	8,080
12 Months or Greater, Unrealized Losses	(2,165)	(1,695)
Total, Fair Value	49,578	136,791
Total, Unrealized Losses	(2,165)	(10,944)
Foreign Governments [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	0	9,997
Gross Unrealized Gains	0	159
Gross Unrealized Losses	0	0
Fair Value	0	10,156
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Total, Unrealized Losses	0	0
Public Utilities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	862,772	864,324
Gross Unrealized Gains	67,976	53,222
Gross Unrealized Losses	(1,040)	(9,687)
Fair Value	929,708	907,859
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	260,982
Less than 12 Months, Unrealized Losses	0	(8,998)
12 Months or Greater, Fair Value	68,885	7,821
12 Months or Greater, Unrealized Losses	(1,040)	(689)
Total, Fair Value	68,885	268,803
Total, Unrealized Losses	(1,040)	(9,687)
Corporate [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,595,636	3,463,521
Gross Unrealized Gains	206,319	153,442
Gross Unrealized Losses	(19,883)	(81,760)
Fair Value	3,782,072	3,535,203
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	67,941	1,335,088
Less than 12 Months, Unrealized Losses	(36)	(71,330)
12 Months or Greater, Fair Value	855,865	117,179
12 Months or Greater, Unrealized Losses	(19,847)	(10,430)
Total, Fair Value	923,806	1,452,267
Total, Unrealized Losses	(19,883)	(81,760)
Mortgage-backed [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,700,161	1,696,887
Gross Unrealized Gains	67,049	54,035
Gross Unrealized Losses	(12,735)	(33,376)
Fair Value	1,754,475	1,717,546
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	76,145	581,373
Less than 12 Months, Unrealized Losses	(310)	(32,043)
12 Months or Greater, Fair Value	272,530	13,861
12 Months or Greater, Unrealized Losses	(12,425)	(1,333)
Total, Fair Value	348,675	595,234
Total, Unrealized Losses	(12,735)	(33,376)
Home Equity [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	19,762	20,179
Gross Unrealized Gains	4,907	4,738
Gross Unrealized Losses	0	(32)
Fair Value	24,669	24,885
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value		0
Less than 12 Months, Unrealized Losses		0
12 Months or Greater, Fair Value		2,617
12 Months or Greater, Unrealized Losses		(32)
Total, Fair Value		2,617
Total, Unrealized Losses	0	(32)
Manufactured Housing [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,099	7,125
Gross Unrealized Gains	353	460
Gross Unrealized Losses	0	0
Fair Value	6,452	7,585
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Total, Unrealized Losses	$ 0	$ 0