Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income:
Loans, including fees	$ 1,226,648	$ 1,064,276	$ 944,233
Investment securities available for sale	96,928	82,699	67,467
Mortgage loans held for sale	1,950	1,926	2,646
Federal Reserve Bank balances	10,156	6,470	4,356
Other earning assets	8,623	7,126	4,101
Total interest income	1,344,305	1,162,497	1,022,803
Interest expense:
Deposits	143,871	81,325	64,206
Federal funds purchased, securities sold under repurchase agreements, and other short-term borrowings	3,553	950	501
Long-term debt	48,468	56,913	58,916
Total interest expense	195,892	139,188	123,623
Net interest income	1,148,413	1,023,309	899,180
Provision for loan losses	51,697	67,185	28,000
Net interest income after provision for loan losses	1,096,716	956,124	871,180
Non-interest income:
Revenue from contract with customer	223,032
Income from bank-owned life insurance	15,403	13,460	11,364
Cabela's Transaction Fee	0	75,000	0
Investment securities (losses) gains, net	(1,296)	(289)	6,011
Other non-interest income	12,459	13,205	15,170
Total non-interest income	280,093	345,327	273,194
Non-interest expense:
Salaries and other personnel expense	453,420	433,321	402,026
Net occupancy and equipment expense	130,482	119,964	109,347
Third-party processing expense	58,625	54,708	46,320
FDIC insurance and other regulatory fees	24,494	27,011	26,714
Professional fees	26,737	26,232	26,698
Advertising expense	20,881	22,948	20,264
Foreclosed real estate expense, net	2,204	12,540	12,838
Loss on early extinguishment of debt, net	0	23,160	4,735
Earnout liability adjustments	11,652	5,466	0
Merger-related expense	10,065	110	1,636
Other operating expenses	90,895	95,853	105,345
Total non-interest expense	829,455	821,313	755,923
Income before income taxes	547,354	480,138	388,451
Income tax expense	118,878	204,664	141,667
Net income	428,476	275,474	246,784
Less: Preferred stock dividends and redemption charge	17,998	10,238	10,238
Net income available to common shareholders	$ 410,478	$ 265,236	$ 236,546
Net income per common share, basic (in dollars per share)	$ 3.49	$ 2.19	$ 1.90
Net income per common share, diluted (in dollars per share)	$ 3.47	$ 2.17	$ 1.89
Weighted average common shares outstanding, basic (in shares)	117,644	121,162	124,389
Weighted average common shares outstanding, diluted (in shares)	118,378	122,012	125,078
Service charges on deposit accounts
Non-interest income:
Revenue from contract with customer	$ 80,840	$ 81,419	$ 83,246
Fiduciary and asset management fees
Non-interest income:
Revenue from contract with customer	54,685	50,485	46,594
Card fees
Non-interest income:
Revenue from contract with customer	42,503	39,376	39,302
Brokerage revenue
Non-interest income:
Revenue from contract with customer	36,567	29,705	27,028
Mortgage banking income
Non-interest income:
Revenue from contract with customer	18,958	22,798	24,259
Other fee income
Non-interest income:
Revenue from contract with customer	$ 19,974	$ 20,168	$ 20,220