Investments (Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	$ 2,563,976	$ 2,524,118
Gross Unrealized Gains, Debt securities	152,691	144,950
Gross Unrealized Losses, Debt securities	(9,402)	(32,402)
Fair Value, Debt securities	2,707,265	2,636,666
Amortized Cost, Equity securities		11,146
Gross Unrealized Gains, Equity securities		4,489
Gross Unrealized Losses, Equity securities		(757)
Fair Value, Equity securities		14,878
Amortized Cost	2,576,805	2,535,264
Gross Unrealized Gains	157,906	149,439
Gross Unrealized Losses	(9,831)	(33,159)
Securities available for sale, at fair value (cost: $2,576,805 and $2,535,264)	2,724,880	2,651,544
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	182,869	570,715
Less than 12 Months, Unrealized Losses	(1,385)	(28,639)
12 Months or Greater, Fair Value	276,462	47,633
12 Months or Greater, Unrealized Losses	(8,446)	(4,520)
Total, Fair Value	459,331	618,348
Total, Unrealized Losses	(9,831)	(33,159)
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, at fair value (cost: $2,576,805 and $2,535,264)	2,707,265	2,636,666
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	180,872	567,008
Less than 12 Months, Unrealized Losses	(1,269)	(27,882)
12 Months or Greater, Fair Value	272,842	47,633
12 Months or Greater, Unrealized Losses	(8,133)	(4,520)
Total, Fair Value	453,714	614,641
Total, Unrealized Losses	(9,402)	(32,402)
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	591	594
Gross Unrealized Gains, Debt securities	0	0
Gross Unrealized Losses, Debt securities	(38)	(110)
Fair Value, Debt securities	553	484
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	553	484
12 Months or Greater, Unrealized Losses	(38)	(110)
Total, Fair Value	553	484
Total, Unrealized Losses	(38)	(110)
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	9,937	9,931
Gross Unrealized Gains, Debt securities	313	0
Gross Unrealized Losses, Debt securities	0	(156)
Fair Value, Debt securities	10,250	9,775
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value		9,775
Less than 12 Months, Unrealized Losses		(156)
12 Months or Greater, Fair Value		0
12 Months or Greater, Unrealized Losses		0
Total, Fair Value		9,775
Total, Unrealized Losses		(156)
Public Utilities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	189,636	233,788
Gross Unrealized Gains, Debt securities	11,994	15,014
Gross Unrealized Losses, Debt securities	(406)	(1,397)
Fair Value, Debt securities	201,224	247,405
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	20,090
Less than 12 Months, Unrealized Losses	0	(1,343)
12 Months or Greater, Fair Value	18,556	962
12 Months or Greater, Unrealized Losses	(406)	(54)
Total, Fair Value	18,556	21,052
Total, Unrealized Losses	(406)	(1,397)
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,296,848	2,195,124
Gross Unrealized Gains, Debt securities	135,520	124,519
Gross Unrealized Losses, Debt securities	(8,955)	(30,732)
Fair Value, Debt securities	2,423,413	2,288,911
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	180,872	532,310
Less than 12 Months, Unrealized Losses	(1,269)	(26,376)
12 Months or Greater, Fair Value	248,901	46,187
12 Months or Greater, Unrealized Losses	(7,686)	(4,356)
Total, Fair Value	429,773	578,497
Total, Unrealized Losses	(8,955)	(30,732)
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	52,270	68,799
Gross Unrealized Gains, Debt securities	4,541	5,040
Gross Unrealized Losses, Debt securities	0	0
Fair Value, Debt securities	56,811	73,839
Home Equity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	11,817	12,079
Gross Unrealized Gains, Debt securities	237	245
Gross Unrealized Losses, Debt securities	(3)	(7)
Fair Value, Debt securities	12,051	12,317
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	0	4,833
Less than 12 Months, Unrealized Losses	0	(7)
12 Months or Greater, Fair Value	4,832	0
12 Months or Greater, Unrealized Losses	(3)	0
Total, Fair Value	4,832	4,833
Total, Unrealized Losses	(3)	(7)
Manufactured Housing [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Debt securities	2,877	3,803
Gross Unrealized Gains, Debt securities	86	132
Gross Unrealized Losses, Debt securities	0	0
Fair Value, Debt securities	2,963	3,935
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, at fair value (cost: $2,576,805 and $2,535,264)	17,615	14,878
Equity Public [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Equity securities	12,829
Gross Unrealized Gains, Equity securities	5,215
Gross Unrealized Losses, Equity securities	(429)
Fair Value, Equity securities	17,615
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	1,997	3,707
Less than 12 Months, Unrealized Losses	(116)	(757)
12 Months or Greater, Fair Value	3,620	0
12 Months or Greater, Unrealized Losses	(313)	0
Total, Fair Value	5,617	3,707
Total, Unrealized Losses	$ (429)	$ (757)