Mortgage Banking Activities, Mortgage Servicing Rights (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced	139,340	131,859	117,483
Outstanding principal balance of residential mortgage loans serviced for others	$ 21,997,568,000	$ 19,678,226,000	$ 16,162,887,000
Weighted average interest rate (in hundredths)	3.97%	4.12%	4.29%
Remaining contractual term (in months)	301 months	300 months	296 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 218,605,000	$ 171,976,000	$ 153,333,000
Additions, net	71,405,000	79,546,000	54,413,000
Change in fair value due to loan runoff	(40,744,000)	(28,064,000)	(19,325,000)
Change in fair value due to market changes	(2,193,000)	(4,853,000)	(16,445,000)
Ending balance	$ 247,073,000	$ 218,605,000	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)	10.08%	10.11%
Prepayment rate - based upon loan interest rate, original term and loan type, Minimum	8.98%	7.41%
Prepayment rate - based upon loan interest rate, original term and loan type, Maximum	16.91%	23.88%
Loan servicing costs - annually per loan based upon loan type, Performing, minimum (in dollars per loan)	$ 63	$ 63
Loan servicing costs - annually per loan based upon loan type, Performing, maximum (in dollars per loan)	120	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)	650	650
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Maximum (in dollars per loan)	$ 4,250	$ 4,250
Primary secondary mortgage rate spread	105	130
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)	1.98%	1.73%
Interest Rate Sensitivity of Mortgage Servicing Rights [Abstract]
Economic hedge threshold for interest rate sensitivity for mortgage servicing rights and securities held (in basis points)	50
Dollar increase in fair value of mortgage servicing rights due to 50 basis point increase in mortgage interest rates	$ 25,000,000
Dollar decrease in fair value of mortgage servicing rights due to 50 basis point decrease in mortgage interest rates	29,000,000
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	9,911,000	$ 11,114,000	15,935,000
Additions, net	0	0	0
Change in fair value due to loan runoff	(2,844,000)	(2,645,000)	(2,357,000)
Change in fair value due to market changes	1,842,000	1,442,000	(2,464,000)
Ending balance	8,909,000	9,911,000	11,114,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	208,694,000	160,862,000	137,398,000
Additions, net	71,405,000	79,546,000	54,413,000
Change in fair value due to loan runoff	(37,900,000)	(25,419,000)	(16,968,000)
Change in fair value due to market changes	(4,035,000)	(6,295,000)	(13,981,000)
Ending balance	$ 238,164,000	$ 208,694,000	$ 160,862,000