Mortgage Banking Activities, Mortgage Servicing Rights (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced	131,859	117,483	106,137
Outstanding principal balance of residential mortgage loans serviced for others	$ 19,678,226,000	$ 16,162,887,000	$ 13,718,942,000
Weighted average interest rate (in hundredths)	4.12%	4.29%	4.40%
Remaining contractual term (in months)	300 months	296 months	292 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 171,976,000	$ 153,333,000	$ 100,812,000
Additions, net	79,546,000	54,413,000	49,431,000
Change in fair value due to loan runoff	(28,064,000)	(19,325,000)	(19,630,000)
Change in fair value due to market changes	(4,853,000)	(16,445,000)	22,720,000
Ending balance	$ 218,605,000	$ 171,976,000	153,333,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)	10.11%	10.17%
Servicing Assets At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed Minimum	7.41%	7.70%
Servicing Assets At Fair Value Assumptions Used To Estimate Fair Value Prepayment Speed Maximum	23.88%	30.44%
Loan servicing costs - annually per loan based upon loan type, Performing, minimum (in dollars per loan)	$ 63	$ 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)	650	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)	1.73%	1.77%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 11,114,000	$ 15,935,000	12,976,000
Additions, net	0	0	0
Change in fair value due to loan runoff	(2,645,000)	(2,357,000)	(3,029,000)
Change in fair value due to market changes	1,442,000	(2,464,000)	5,988,000
Ending balance	9,911,000	11,114,000	15,935,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	160,862,000	137,398,000	87,836,000
Additions, net	79,546,000	54,413,000	49,431,000
Change in fair value due to loan runoff	(25,419,000)	(16,968,000)	(16,601,000)
Change in fair value due to market changes	(6,295,000)	(13,981,000)	16,732,000
Ending balance	$ 208,694,000	$ 160,862,000	$ 137,398,000