Mortgage Banking Activities, Mortgage Servicing Rights (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced	101,498	96,772	101,498	96,772	98,246
Outstanding principal balance of residential mortgage loans serviced for others	$ 12,741,651,000	$ 11,564,643,000	$ 12,741,651,000	$ 11,564,643,000	$ 11,981,624,000
Weighted average interest rate (in hundredths)			4.47%	4.99%	4.71%
Remaining term (in months)	291 months	289 months	291 months	289 months	289 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	109,840,000	98,138,000	100,812,000	86,783,000	86,783,000
Additions, net	14,499,000	9,275,000	25,932,000	17,647,000
Change in fair value due to loan runoff	(5,765,000)	(4,180,000)	(10,828,000)	(8,324,000)
Change in fair value due to market changes	14,315,000	(11,450,000)	16,973,000	(4,323,000)
Ending balance	132,889,000	91,783,000	132,889,000	91,783,000	100,812,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)			10.25%	10.33%	10.29%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, minimum (in hundredths)			7.00%	11.44%	8.38%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, maximum (in hundredths)			32.30%	53.10%	43.94%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)			58	55	55
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)			105	105	105
Loan servicing costs - annually per loan based upon loan type, delinquent, minimum (in dollars per loan)			135	135	135
Loan servicing costs - annually per loan based upon loan type, delinquent, maximum (in dollars per loan)			500	500	500
Loan servicing costs - annually per loan based upon loan type, foreclosure, minimum (in dollars per loan)			875	875	875
Loan servicing costs - annually per loan based upon loan type, foreclosure, maximum (in dollars per loan)			4,250	3,750	4,250
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)			1.56%	1.28%	0.87%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	13,203,000	21,204,000	12,976,000	18,903,000	18,903,000
Additions, net	0	0	0	0
Change in fair value due to loan runoff	(940,000)	(950,000)	(1,811,000)	(1,960,000)
Change in fair value due to market changes	3,319,000	(3,893,000)	4,417,000	(582,000)
Ending balance	15,582,000	16,361,000	15,582,000	16,361,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	96,637,000	76,934,000	87,836,000	67,880,000	67,880,000
Additions, net	14,499,000	9,275,000	25,932,000	17,647,000
Change in fair value due to loan runoff	(4,825,000)	(3,230,000)	(9,017,000)	(6,364,000)
Change in fair value due to market changes	10,996,000	(7,557,000)	12,556,000	(3,741,000)
Ending balance	$ 117,307,000	$ 75,422,000	$ 117,307,000	$ 75,422,000