Mortgage Banking Activities, Mortgage Servicing Rights (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced		117,483	106,137	98,246
Outstanding principal balance of residential mortgage loans serviced for others		$ 16,162,887,000	$ 13,718,942,000	$ 11,981,624,000
Weighted average interest rate (in hundredths)		4.29%	4.40%	4.71%
Remaining term (in months)		296 months	292 months	289 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance		153,333,000	100,812,000	86,783,000
Additions, net		54,413,000	49,431,000	42,191,000
Change in fair value due to loan runoff		(19,325,000)	(19,630,000)	(18,952,000)
Change in fair value due to market changes		(16,445,000)	22,720,000	(9,210,000)
Ending balance		171,976,000	153,333,000	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)		10.17%	10.21%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, minimum (in hundredths)		7.70%	6.66%
Prepayment rate - estimated based upon loan interest rate, original term and loan type, maximum (in hundredths)		30.44%	26.19%
Loan servicing costs - annually per loan based upon loan type, Performing, minimum (in dollars per loan)		60	60
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)		150	150
Loan servicing costs - annually per loan based upon loan type, Delinquent loans, Maximum (in dollars per loan)		500	500
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Minimum (in dollars per loan)		1,000	1,000
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Maximum (in dollars per loan)		4,250	4,250
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)		1.77%	1.80%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance		15,935,000	12,976,000	18,903,000
Additions, net		0	0	0
Change in fair value due to loan runoff		(2,357,000)	(3,029,000)	(4,164,000)
Change in fair value due to market changes		(2,464,000)	5,988,000	(1,763,000)
Ending balance		11,114,000	15,935,000	12,976,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance		137,398,000	87,836,000	67,880,000
Additions, net		54,413,000	49,431,000	42,191,000
Change in fair value due to loan runoff		(16,968,000)	(16,601,000)	(14,788,000)
Change in fair value due to market changes		(13,981,000)	16,732,000	(7,447,000)
Ending balance		$ 160,862,000	$ 137,398,000	$ 87,836,000