Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Loans, including fees	$ 1,064,276	$ 944,233	$ 877,384
Investment securities available for sale	82,699	67,467	59,154
Trading account assets	141	91	303
Mortgage loans held for sale	1,926	2,646	2,546
Federal Reserve Bank balances	6,470	4,356	3,144
Other earning assets	6,985	4,010	3,431
Total interest income	1,162,497	1,022,803	945,962
Interest expense:
Deposits	81,325	64,206	65,534
Federal funds purchased and securities sold under repurchase agreements	198	200	168
Long-term debt	57,665	59,217	52,942
Total interest expense	139,188	123,623	118,644
Net interest income	1,023,309	899,180	827,318
Provision for loan losses	67,185	28,000	19,010
Net interest income after provision for loan losses	956,124	871,180	808,308
Non-interest income:
Service charges on deposit accounts	79,801	81,425	80,142
Fiduciary and asset management fees	50,485	46,594	45,928
Brokerage revenue	29,705	27,028	27,855
Mortgage banking income	22,798	24,259	24,096
Bankcard fees	32,232	33,318	33,172
Cabela's Transaction Fee	75,000	0	0
Investment securities (losses) gains, net	(289)	6,011	2,769
Decrease in fair value of private equity investments, net	(3,093)	(1,026)	(219)
Other fee income	20,168	20,220	21,170
Other non-interest income	38,520	35,365	33,007
Total non-interest income	345,327	273,194	267,920
Non-interest expense:
Salaries and other personnel expense	433,321	402,026	380,918
Net occupancy and equipment expense	119,964	109,347	107,466
Third-party processing expense	54,708	46,320	42,851
FDIC insurance and other regulatory fees	27,011	26,714	27,091
Professional fees	26,232	26,698	26,646
Advertising expense	22,948	20,264	15,477
Foreclosed real estate expense, net	12,540	12,838	22,803
Loss on early extinguishment of debt, net	23,160	4,735	1,533
Earnout liability adjustments	5,466	0	0
Fair value adjustment to Visa derivative		5,795	1,464
Restructuring charges, net	7,014	8,267	36
Other operating expenses	88,949	92,919	91,370
Total non-interest expense	821,313	755,923	717,655
Income before income taxes	480,138	388,451	358,573
Income tax expense	204,664	141,667	132,491
Net income	275,474	246,784	226,082
Dividends on preferred stock	10,238	10,238	10,238
Net income available to common shareholders	$ 265,236	$ 236,546	$ 215,844
Net income per common share, basic (in dollars per share)	$ 2.19	$ 1.90	$ 1.63
Net income per common share, diluted (in dollars per share)	$ 2.17	$ 1.89	$ 1.62
Weighted average common shares outstanding, basic	121,162	124,389	132,423
Weighted average common shares outstanding, diluted	122,012	125,078	133,201