Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	139,587	131,859	128,828	139,587	128,828
Outstanding principal balance of residential mortgage loans serviced for others	$ 21,851,536,000	$ 19,678,226,000	$ 18,928,726,000	$ 21,851,536,000	$ 18,928,726,000
Weighted average interest rate	4.01%	4.12%	4.15%	4.01%	4.15%
Remaining term (in months)	302 months	300 months	300 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 190,747,000	$ 200,049,000	$ 198,694,000	$ 218,605,000	$ 171,976,000
Additions, net	21,990,000		19,993,000	56,345,000	62,375,000
Change in fair value due to scheduled payments and full-balance payoffs	(11,443,000)		(6,881,000)	(29,385,000)	(22,033,000)
Change in fair value due to market assumption changes	2,327,000		(11,757,000)	(41,944,000)	(12,269,000)
Ending balance	$ 203,621,000	$ 218,605,000	$ 200,049,000	$ 203,621,000	$ 200,049,000
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%	10.12%
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	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	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)	1.18%	1.73%	1.40%
Primary secondary mortgage rate spread (in basis points)	115	130	135	115	135
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 4,067,000	$ 9,413,000	$ 10,730,000	$ 9,911,000	$ 11,114,000
Additions, net	0		0	0	0
Change in fair value due to scheduled payments and full-balance payoffs	(753,000)		(661,000)	(2,109,000)	(2,171,000)
Change in fair value due to market assumption changes	251,000		(656,000)	(4,237,000)	470,000
Ending balance	3,565,000	9,911,000	9,413,000	3,565,000	9,413,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	186,680,000	190,636,000	187,964,000	208,694,000	160,862,000
Additions, net	21,990,000		19,993,000	56,345,000	62,375,000
Change in fair value due to scheduled payments and full-balance payoffs	(10,690,000)		(6,220,000)	(27,276,000)	(19,862,000)
Change in fair value due to market assumption changes	2,076,000		(11,101,000)	(37,707,000)	(12,739,000)
Ending balance	$ 200,056,000	$ 208,694,000	$ 190,636,000	$ 200,056,000	$ 190,636,000