Mortgage Banking Activities, Mortgage Servicing Rights (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced	104,115	97,465	104,115	97,465	98,246
Outstanding principal balance of residential mortgage loans serviced for others	$ 13,298,479,000	$ 11,756,350,000	$ 13,298,479,000	$ 11,756,350,000	$ 11,981,624,000
Weighted average interest rate (in hundredths)	4.42%	4.85%	4.42%	4.85%	4.71%
Remaining term (in months)	292 months	289 months	292 months	289 months	289 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance			100,812,000	86,783,000	86,783,000	132,889,000	91,783,000
Additions, net	13,225,000	12,107,000	39,157,000	29,754,000
Change in fair value due to loan runoff	(4,905,000)	(4,661,000)	(15,733,000)	(12,985,000)
Change in fair value due to market changes	(346,000)	(9,576,000)	16,627,000	(13,899,000)
Ending balance	140,863,000	89,653,000	140,863,000	89,653,000	100,812,000	132,889,000	91,783,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)			10.23%	10.32%	10.29%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, minimum (in hundredths)			7.03%	9.14%	8.38%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, maximum (in hundredths)			30.92%	46.42%	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)			1.54%	0.77%	0.87%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance			12,976,000	18,903,000	18,903,000	15,582,000	16,361,000
Additions, net	0	0	0	0
Change in fair value due to loan runoff	(693,000)	(998,000)	(2,504,000)	(2,958,000)
Change in fair value due to market changes	(76,000)	(2,648,000)	4,341,000	(3,230,000)
Ending balance	14,813,000	12,715,000	14,813,000	12,715,000		15,582,000	16,361,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance			87,836,000	67,880,000	67,880,000	117,307,000	75,422,000
Additions, net	13,225,000	12,107,000	39,157,000	29,754,000
Change in fair value due to loan runoff	(4,212,000)	(3,663,000)	(13,229,000)	(10,027,000)
Change in fair value due to market changes	(270,000)	(6,928,000)	12,286,000	(10,669,000)
Ending balance	$ 126,050,000	$ 76,938,000	$ 126,050,000	$ 76,938,000		$ 117,307,000	$ 75,422,000