Mortgage Banking Activities, Mortgage Servicing Rights (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2010	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced			98,246	95,841	96,443
Outstanding principal balance of residential mortgage loans serviced for others			$ 11,981,624,000	$ 11,300,986,000	$ 11,194,582,000
Weighted average interest rate (in hundredths)			4.71%	5.19%	5.44%
Remaining term (in months)			289 months	290 months	292 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	73,824,000	115,723,000	86,783,000	115,723,000	73,824,000
Additions, net			42,191,000	26,251,000	58,924,000
Servicing Asset at Fair Value, Other Changes that Affect Balance					11,832,000
Change in fair value due to loan runoff			(18,952,000)	(14,744,000)	(20,686,000)
Change in fair value due to market changes			(9,210,000)	(40,447,000)	(8,171,000)
Ending balance			100,812,000	86,783,000	115,723,000
Number of mortgage loans for which servicing rights were purchased	34,000
Outstanding principal balance of mortgage loans for which servicing rights were purchased	4,200,000,000
Purchase price of acquired mortgage servicing rights	32,000,000
Acquisition date fair value of mortgage servicing rights	43,700,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)			10.29%	10.34%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, minimum (in hundredths)			8.38%	10.88%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, maximum (in hundredths)			43.94%	49.68%
Loan servicing costs - annually per loan based upon loan type, Performing, minimum (in dollars per loan)			55	55
Loan servicing costs - annually per loan based upon loan type, Performing, maximum (in dollars per loan)			105	105
Loan servicing costs - annually per loan based upon loan type, Delinquent loans, Minimum (in dollars per loan)			135	50
Loan servicing costs - annually per loan based upon loan type, Delinquent loans, Maximum (in dollars per loan)			500	250
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Minimum (in dollars per loan)			875	500
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Maximum (in dollars per loan)			4,250	3,000
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)			0.87%	1.21%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	7,828,000	37,900,000	18,903,000	37,900,000	7,828,000
Additions, net			0	0	31,321,000
Servicing Asset at Fair Value, Other Changes that Affect Balance					11,832,000
Change in fair value due to loan runoff			(4,164,000)	(4,699,000)	(6,791,000)
Change in fair value due to market changes			(1,763,000)	(14,298,000)	(6,290,000)
Ending balance			12,976,000	18,903,000	37,900,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	65,996,000	77,823,000	67,880,000	77,823,000	65,996,000
Additions, net			42,191,000	26,251,000	27,603,000
Servicing Asset at Fair Value, Other Changes that Affect Balance					0
Change in fair value due to loan runoff			(14,788,000)	(10,045,000)	(13,895,000)
Change in fair value due to market changes			(7,447,000)	(26,149,000)	(1,881,000)
Ending balance			$ 87,836,000	$ 67,880,000	$ 77,823,000