Investments (Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,568,512	$ 2,422,650
Gross Unrealized Gains	262,150	211,607
Gross Unrealized Losses	(4,661)	(9,304)
Fair Value	2,826,001	2,624,953
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	85,196	124,570
Less than 12 Months, Unrealized Losses	(1,076)	(5,189)
12 Months or Greater, Fair Value	21,070	28,851
12 Months or Greater, Unrealized Losses	(3,585)	(4,115)
Total, Fair Value	106,266	153,421
Total, Unrealized Losses	(4,661)	(9,304)
Debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,559,052	2,416,148
Gross Unrealized Gains	259,285	201,418
Gross Unrealized Losses	(4,603)	(9,159)
Fair Value	2,813,734	2,608,407
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	84,440	123,848
Less than 12 Months, Unrealized Losses	(1,068)	(5,105)
12 Months or Greater, Fair Value	20,775	28,552
12 Months or Greater, Unrealized Losses	(3,535)	(4,054)
Total, Fair Value	105,215	152,400
Total, Unrealized Losses	(4,603)	(9,159)
U.S. Agencies [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	0	0
Total, Unrealized Losses	0	0
U.S. Treasury [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	0	0
Total, Unrealized Losses	0	0
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	599	4,042
Gross Unrealized Gains	0	16
Gross Unrealized Losses	(28)	(170)
Fair Value	571	3,888
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	571	0
Less than 12 Months, Unrealized Losses	(28)	0
12 Months or Greater, Fair Value	0	2,257
12 Months or Greater, Unrealized Losses	0	(170)
Total, Fair Value	571	2,257
Total, Unrealized Losses	(28)	(170)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	15,134	20,145
Gross Unrealized Gains	932	588
Gross Unrealized Losses	0	0
Fair Value	16,066	20,733
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	0	0
Total, Unrealized Losses	0	0
Public Utilities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	254,853	327,794
Gross Unrealized Gains	26,621	32,511
Gross Unrealized Losses	(47)	(907)
Fair Value	281,427	359,398
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	10,949	19,314
Less than 12 Months, Unrealized Losses	(47)	(907)
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	10,949	19,314
Total, Unrealized Losses	(47)	(907)
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,157,706	1,881,735
Gross Unrealized Gains	222,587	155,144
Gross Unrealized Losses	(2,981)	(5,839)
Fair Value	2,377,312	2,031,040
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	64,383	100,584
Less than 12 Months, Unrealized Losses	(713)	(4,009)
12 Months or Greater, Fair Value	14,713	20,944
12 Months or Greater, Unrealized Losses	(2,268)	(1,830)
Total, Fair Value	79,096	121,528
Total, Unrealized Losses	(2,981)	(5,839)
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	113,488	163,856
Gross Unrealized Gains	8,905	12,389
Gross Unrealized Losses	(64)	(189)
Fair Value	122,329	176,056
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	3,839	3,950
Less than 12 Months, Unrealized Losses	(64)	(189)
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	3,839	3,950
Total, Unrealized Losses	(64)	(189)
Home Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	12,242	10,887
Gross Unrealized Gains	0	30
Gross Unrealized Losses	(1,483)	(2,054)
Fair Value	10,759	8,863
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	4,698	0
Less than 12 Months, Unrealized Losses	(216)	0
12 Months or Greater, Fair Value	6,062	5,351
12 Months or Greater, Unrealized Losses	(1,267)	(2,054)
Total, Fair Value	10,760	5,351
Total, Unrealized Losses	(1,483)	(2,054)
Manufactured Housing [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	5,030	7,689
Gross Unrealized Gains	240	740
Gross Unrealized Losses	0	0
Fair Value	5,270	8,429
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	0	0
Total, Unrealized Losses	0	0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	12,267	16,546
Equity Private [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Equity securities	0	195
Gross Unrealized Gains	0	7,923
Gross Unrealized Losses	0	0
Fair Value	0	8,118
Equity Public [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Equity securities	9,460	6,307
Gross Unrealized Gains	2,865	2,266
Gross Unrealized Losses	(58)	(145)
Fair Value	12,267	8,428
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	756	722
Less than 12 Months, Unrealized Losses	(8)	(84)
12 Months or Greater, Fair Value	295	299
12 Months or Greater, Unrealized Losses	(50)	(61)
Total, Fair Value	1,051	1,021
Total, Unrealized Losses	$ (58)	$ (145)