Investments (Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,560,225	$ 2,422,650
Gross Unrealized Gains	265,931	211,607
Gross Unrealized Losses	(4,789)	(9,304)
Fair Value	2,821,367	2,624,953
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	49,416	124,570
Less than 12 Months, Unrealized Losses	(2,256)	(5,189)
12 Months or Greater, Fair Value	37,189	28,851
12 Months or Greater, Unrealized Losses	(2,533)	(4,115)
Total, Fair Value	86,605	153,421
Total, Unrealized Losses	(4,789)	(9,304)
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,550,665	2,416,148
Gross Unrealized Gains	263,113	201,418
Gross Unrealized Losses	(4,716)	(9,159)
Fair Value	2,809,062	2,608,407
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	46,781	123,848
Less than 12 Months, Unrealized Losses	(2,234)	(5,105)
12 Months or Greater, Fair Value	36,849	28,552
12 Months or Greater, Unrealized Losses	(2,482)	(4,054)
Total, Fair Value	83,630	152,400
Total, Unrealized Losses	(4,716)	(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	11	16
Gross Unrealized Losses	0	(170)
Fair Value	610	3,888
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	2,257
12 Months or Greater, Unrealized Losses	0	(170)
Total, Fair Value	0	2,257
Total, Unrealized Losses	0	(170)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	15,136	20,145
Gross Unrealized Gains	965	588
Gross Unrealized Losses	0	0
Fair Value	16,101	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	258,889	327,794
Gross Unrealized Gains	27,574	32,511
Gross Unrealized Losses	0	(907)
Fair Value	286,463	359,398
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	19,314
Less than 12 Months, Unrealized Losses	0	(907)
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	0	19,314
Total, Unrealized Losses	0	(907)
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,135,990	1,881,735
Gross Unrealized Gains	224,001	155,144
Gross Unrealized Losses	(2,644)	(5,839)
Fair Value	2,357,347	2,031,040
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	34,346	100,584
Less than 12 Months, Unrealized Losses	(1,625)	(4,009)
12 Months or Greater, Fair Value	30,940	20,944
12 Months or Greater, Unrealized Losses	(1,019)	(1,830)
Total, Fair Value	65,286	121,528
Total, Unrealized Losses	(2,644)	(5,839)
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	122,348	163,856
Gross Unrealized Gains	10,320	12,389
Gross Unrealized Losses	(251)	(189)
Fair Value	132,417	176,056
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	7,872	3,950
Less than 12 Months, Unrealized Losses	(251)	(189)
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	7,872	3,950
Total, Unrealized Losses	(251)	(189)
Home Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	12,293	10,887
Gross Unrealized Gains	0	30
Gross Unrealized Losses	(1,821)	(2,054)
Fair Value	10,472	8,863
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	4,563	0
Less than 12 Months, Unrealized Losses	(358)	0
12 Months or Greater, Fair Value	5,909	5,351
12 Months or Greater, Unrealized Losses	(1,463)	(2,054)
Total, Fair Value	10,472	5,351
Total, Unrealized Losses	(1,821)	(2,054)
Manufactured Housing [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	5,410	7,689
Gross Unrealized Gains	242	740
Gross Unrealized Losses	0	0
Fair Value	5,652	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	12,305	16,546
Equity Private [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Equity securities		195
Gross Unrealized Gains		7,923
Gross Unrealized Losses		0
Fair Value		8,118
Equity Public [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Equity securities	9,560	6,307
Gross Unrealized Gains	2,818	2,266
Gross Unrealized Losses	(73)	(145)
Fair Value	12,305	8,428
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	2,635	722
Less than 12 Months, Unrealized Losses	(22)	(84)
12 Months or Greater, Fair Value	340	299
12 Months or Greater, Unrealized Losses	(51)	(61)
Total, Fair Value	2,975	1,021
Total, Unrealized Losses	$ (73)	$ (145)