Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	138,778	139,340	134,040
Outstanding principal balance of residential mortgage loans serviced for others	$ 22,015,021,000	$ 21,997,568,000	$ 20,294,662,000
Weighted average interest rate	3.96%	3.97%	4.10%
Remaining term (in months)	300 months	301 months	300 months
Economic hedge threshold for interest rate sensitivity for mortgage servicing rights and securities held (in basis points)	50
Dollar decrease in fair value of mortgage servicing rights due to a 50 basis point decrease in mortgage interest rates	$ 30,000,000
Dollar increase in fair value of mortgage servicing rights Due To 50 Basis Point Increase In Mortgage Interest Rates	25,000,000
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	247,073,000		$ 218,605,000
Additions, net	8,436,000		13,582,000
Change in fair value due to scheduled payments and full-balance payoffs	(7,962,000)		(8,144,000)
Change in fair value due to market assumption changes	1,856,000		(27,988,000)
Ending balance	$ 249,403,000	$ 247,073,000	$ 196,055,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)	10.08%	10.08%	10.11%
Prepayment rate - based upon loan interest rate, original term and loan type, minimum	8.66%	8.98%	8.88%
Prepayment rate - based upon loan interest rate, original term and loan type, maximum	18.17%	16.91%	35.21%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)	$ 63	$ 63	$ 63
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)	120	120	120
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	650	650
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)	2.06%	1.98%	1.19%
Primary secondary mortgage rate spread (in basis points)	105	105	120
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 8,909,000		$ 9,911,000
Additions, net	0		0
Change in fair value due to scheduled payments and full-balance payoffs	(509,000)		(626,000)
Change in fair value due to market assumption changes	(84,000)		(3,336,000)
Ending balance	8,316,000	$ 8,909,000	5,949,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	238,164,000		208,694,000
Additions, net	8,436,000		13,582,000
Change in fair value due to scheduled payments and full-balance payoffs	(7,453,000)		(7,518,000)
Change in fair value due to market assumption changes	1,940,000		(24,652,000)
Ending balance	$ 241,087,000	$ 238,164,000	$ 190,106,000