Investments And MBS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	$ 1,525,538		$ 1,525,538		$ 1,452,258
Gross Unrealized Gains	27,410		27,410		61,512
Gross Unrealized Losses	(14,068)		(14,068)		(613)
Fair Value	1,538,880		1,538,880		1,513,157
Amortized Cost	185		185		206
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	185		185		206
Gain (Loss) on Investments [Abstract]
Proceeds from Sales			0	362,871
Gross Realized Gains			0	9,537
Gross Realized Losses			0	(74)
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	506,928		506,928		0
Unrealized Losses, Less than 12 months	(13,002)		(13,002)		0
Market Value, 12 months or longer	14,551		14,551		12,921
Unrealized Losses, 12 months or longer	(1,066)		(1,066)		(613)
Market Value, Total	521,479		521,479		12,921
Unrealized Losses, Total	(14,068)		(14,068)		(613)
Other-than-temporary impairment credit losses on securities	0	6,819	0	6,819
Held-to-maturity Securities, Debt Maturities [Abstract]
Amortized Cost, Due within one year	0		0
Amortized Cost, Due after one year through five years	0		0
Amortized Cost, Due afer five years through ten years	0		0
Amortized Cost, Due after ten years	185		185
Amortized Cost, Total	185		185
Estimated Fair Value, Due within one year	0		0
Estimated Fair Value, Due after one year through five years	0		0
Estimated Fair Value, Due after five years through ten years	0		0
Estimated Fair Value, Due after ten years	185		185
Estimated Fair Value, Total	185		185
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Amortized Cost, Due within on year	0		0
Amortized Cost, Due after one year through five years	9,907		9,907
Amortized Cost, Due after five years through ten years	74,756		74,756
Amortized Cost, Due after ten years	1,440,875		1,440,875
Amortized Cost, Total	1,525,538		1,525,538
Estimated Fair Value, Due within one year	0		0
Estimated Fair Value, Due after one year through five years	10,539		10,539
Estimated Fair Value, Due after five years through ten years	74,895		74,895
Estimated Fair Value, Due after ten years	1,453,446		1,453,446
Fair Value	1,538,880		1,538,880		1,513,157
MBS
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	1,337,908		1,337,908		1,263,786
Gross Unrealized Gains	18,264		18,264		45,052
Gross Unrealized Losses	(12,991)		(12,991)		0
Fair Value	1,343,181		1,343,181		1,308,838
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	505,378		505,378		0
Unrealized Losses, Less than 12 months	(12,991)		(12,991)		0
Market Value, 12 months or longer	0		0		0
Unrealized Losses, 12 months or longer	0		0		0
Market Value, Total	505,378		505,378		0
Unrealized Losses, Total	(12,991)		(12,991)		0
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Fair Value	1,343,181		1,343,181		1,308,838
Municipal Bonds
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	187,468		187,468		188,467
Gross Unrealized Gains	9,139		9,139		16,452
Gross Unrealized Losses	(1,077)		(1,077)		(613)
Fair Value	195,530		195,530		204,306
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	1,550		1,550		0
Unrealized Losses, Less than 12 months	(11)		(11)		0
Market Value, 12 months or longer	14,551		14,551		12,921
Unrealized Losses, 12 months or longer	(1,066)		(1,066)		(613)
Market Value, Total	16,101		16,101		12,921
Unrealized Losses, Total	(1,077)		(1,077)		(613)
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Fair Value	195,530		195,530		204,306
Other
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	162		162		5
Gross Unrealized Gains	7		7		8
Gross Unrealized Losses	0		0		0
Fair Value	169		169		13
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	0		0		0
Unrealized Losses, Less than 12 months	0		0		0
Market Value, 12 months or longer	0		0		0
Unrealized Losses, 12 months or longer	0		0		0
Market Value, Total	0		0		0
Unrealized Losses, Total	0		0		0
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Fair Value	169		169		13
Tax Credits
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	185		185		206
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Fair Value	$ 185		$ 185		$ 206