Investments And MBS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	$ 1,418,024		$ 1,452,258
Gross Unrealized Gains	54,301		61,512
Gross Unrealized Losses	(762)		(613)
Estimated Fair Value, Total	1,471,563		1,513,157
Amortized Cost	195		206
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Fair Value	195		206
Gain (Loss) on Investments [Abstract]
Proceeds from Sales	0	178,663
Gross Realized Gains	0	142
Gross Realized Losses	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	32,685		0
Unrealized Losses, Less than 12 months	(172)		0
Market Value, 12 months or longer	14,047		12,921
Unrealized Losses, 12 months or longer	(590)		(613)
Market Value, Total	46,732		12,921
Unrealized Losses, Total	(762)		(613)
Held-to-maturity Securities, Debt Maturities [Abstract]
Amortized Cost, Due within one year	0
Amortized Cost, Due after one year through five years	0
Amortized Cost, Due afer five years through ten years	0
Amortized Cost, Due after ten years	195
Amortized Cost, Total	195
Estimated Fair Value, Due within one year	0
Estimated Fair Value, Due after one year through five years	0
Estimated Fair Value, Due after five years through ten years	0
Estimated Fair Value, Due after ten years	195
Estimated Fair Value, Total	195
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Amortized Cost, Due within on year	0
Amortized Cost, Due after one year through five years	2,720
Amortized Cost, Due after five years through ten years	72,378
Amortized Cost, Due after ten years	1,342,926
Amortized Cost, Total	1,418,024
Estimated Fair Value, Due within one year	0
Estimated Fair Value, Due after one year through five years	2,917
Estimated Fair Value, Due after five years through ten years	75,451
Estimated Fair Value, Due after ten years	1,393,195
Estimated Fair Value, Total	1,471,563		1,513,157
MBS
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	1,229,428		1,263,786
Gross Unrealized Gains	39,074		45,052
Gross Unrealized Losses	(172)		0
Estimated Fair Value, Total	1,268,330		1,308,838
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	32,685		0
Unrealized Losses, Less than 12 months	(172)		0
Market Value, 12 months or longer	0		0
Unrealized Losses, 12 months or longer	0		0
Market Value, Total	32,685		0
Unrealized Losses, Total	(172)		0
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Estimated Fair Value, Total	1,268,330		1,308,838
Municipal Bonds
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	188,434		188,467
Gross Unrealized Gains	15,219		16,452
Gross Unrealized Losses	(590)		(613)
Estimated Fair Value, Total	203,063		204,306
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	0		0
Unrealized Losses, Less than 12 months	0		0
Market Value, 12 months or longer	14,047		12,921
Unrealized Losses, 12 months or longer	(590)		(613)
Market Value, Total	14,047		12,921
Unrealized Losses, Total	(590)		(613)
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Estimated Fair Value, Total	203,063		204,306
Other
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	162		5
Gross Unrealized Gains	8		8
Gross Unrealized Losses	0		0
Estimated Fair Value, Total	170		13
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Market Value, Less than 12 months	0		0
Unrealized Losses, Less than 12 months	0		0
Market Value, 12 months or longer	0		0
Unrealized Losses, 12 months or longer	0		0
Market Value, Total	0		0
Unrealized Losses, Total	0		0
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Estimated Fair Value, Total	170		13
Tax Credits
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Amortized Cost	195		206
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Fair Value	$ 195		$ 206