Mortgage Banking Activities, Mortgage Servicing Rights (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced	97,465	95,831	97,465	95,831	95,841
Outstanding principal balance of residential mortgage loans serviced for others	$ 11,756,350	$ 11,249,503	$ 11,756,350	$ 11,249,503	$ 11,300,986
Weighted average interest rate (in hundredths)			4.85%	5.29%	5.19%
Remaining term (in months)	289	286	289	286	290
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	91,783	109,192	86,783	115,723	115,723
Additions, net	12,107	7,199	29,754	17,966
Change in fair value due to loan runoff	(4,661)	(3,621)	(12,985)	(10,555)
Change in fair value due to market changes	(9,576)	(24,822)	(13,899)	(35,186)
Ending balance	89,653	87,948	89,653	87,948	86,783
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)			10.32%	10.30%	10.34%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, minimum (in hundredths)			9.14%	11.33%	10.88%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, maximum (in hundredths)			46.42%	47.70%	49.68%
Loan servicing costs - annually per loan based upon loan type, minimum (in dollars per loan)			55	55	55
Loan servicing costs - annually per loan based upon loan type, maximum (in dollars per loan)			105	105	105
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)			0.77%	1.26%	1.21%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	16,361	32,866	18,903	37,900	37,900
Additions, net	0	0	0	0
Change in fair value due to loan runoff	(998)	(1,034)	(2,958)	(3,585)
Change in fair value due to market changes	(2,648)	(10,395)	(3,230)	(12,878)
Ending balance	12,715	21,437	12,715	21,437
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	75,422	76,326	67,880	77,823	77,823
Additions, net	12,107	7,199	29,754	17,966
Change in fair value due to loan runoff	(3,663)	(2,587)	(10,027)	(6,970)
Change in fair value due to market changes	(6,928)	(14,427)	(10,669)	(22,308)
Ending balance	$ 76,938	$ 66,511	$ 76,938	$ 66,511

The net increase or decrease in fair value as a result of loan runoff.

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Indicates the number of mortgage loans being serviced.

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Dollar amount of principal outstanding on mortgage loans being serviced.

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The weighted average remaining term of the mortgage loans being serviced.

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The escrow earning rate used to estimate the fair value of servicing assets, based on rates paid on deposit accounts.

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The maximum cost to service a loan for the period used as a variable in estimating fair value.

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The minimum cost to service a loan for the period used as a variable in estimating fair value.

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The maximum estimated speed of prepayments of principal on financial assets which may be one of the factors applied in estimating the fair value of servicing assets.

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The minimum estimated speed of prepayments of principal on financial assets which may be one of the factors applied in estimating the fair value of servicing assets.

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The net increase or decrease in fair value as a result of changes in the assumptions or model used to calculate the fair value of servicing assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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The stated interest rate on the mortgage loan receivable or the weighted average interest rate on a group of loans.

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The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

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Fair value as of the balance sheet date of an asset representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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The discount rate used to estimate the fair value of servicing assets and servicing liabilities.

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