Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	128,828	117,483	114,493	128,828	114,493	117,483
Outstanding principal balance of residential mortgage loans serviced for others	$ 18,928,726,000	$ 16,162,887,000	$ 15,499,653,000	$ 18,928,726,000	$ 15,499,653,000	$ 16,162,887,000
Weighted average interest rate (in hundredths)	4.15%	4.29%	4.33%	4.15%	4.33%	4.29%
Remaining term (in months)	300 months	296 months	295 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 198,694,000	$ 173,286,000	$ 155,740,000	$ 171,976,000	$ 153,333,000	$ 153,333,000
Additions, net	19,993,000		17,367,000	62,375,000	39,183,000
Change in fair value due to loan runoff	(6,881,000)		(5,102,000)	(22,033,000)	(13,606,000)
Change in fair value due to market changes	(11,757,000)		5,281,000	(12,269,000)	(5,624,000)
Ending balance	$ 200,049,000	$ 171,976,000	$ 173,286,000	200,049,000	173,286,000	171,976,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)	10.12%	10.17%	10.17%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)				63	60	60
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)				150	150	150
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)				650	1,000	1,000
Loan servicing costs - annually per loan based upon loan type, foreclosure, maximum (in dollars per loan)				4,250	4,250	4,250
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)	1.40%	1.77%	1.95%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 10,730,000	$ 13,279,000	$ 13,082,000	11,114,000	15,935,000	15,935,000
Additions, net	0		0	0	0
Change in fair value due to loan runoff	(661,000)		(624,000)	(2,171,000)	(1,737,000)
Change in fair value due to market changes	(656,000)		821,000	470,000	(919,000)
Ending balance	9,413,000	11,114,000	13,279,000	9,413,000	13,279,000	11,114,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	187,964,000	160,007,000	142,658,000	160,862,000	137,398,000	137,398,000
Additions, net	19,993,000		17,367,000	62,375,000	39,183,000
Change in fair value due to loan runoff	(6,220,000)		(4,478,000)	(19,862,000)	(11,869,000)
Change in fair value due to market changes	(11,101,000)		4,460,000	(12,739,000)	(4,705,000)
Ending balance	$ 190,636,000	$ 160,862,000	$ 160,007,000	$ 190,636,000	$ 160,007,000	$ 160,862,000