Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income:
Loans, including fees	$ 534,790	$ 521,478	$ 389,535
Investment securities:
Taxable	39,949	35,563	28,165
Tax-exempt	6,186	6,152	5,591
Federal funds sold, securities purchased under agreements to resell and interest-bearing deposits with banks	9,902	4,015	2,709
Total interest income	590,827	567,208	426,000
Interest expense:
Deposits	65,920	45,452	12,353
Federal funds purchased and securities sold under agreements to repurchase	2,627	2,356	1,080
Other borrowings	18,005	6,184	3,581
Total interest expense	86,552	53,992	17,014
Net interest income	504,275	513,216	408,986
Provision for loan losses	12,777	13,783	11,890
Net interest income after provision for loan losses	491,498	499,433	397,096
Noninterest income:
Securities gains (losses), net	2,711	(655)	1,421
Other-than-temporary impairment losses			(753)
Recoveries on acquired loans	6,847	9,117	8,572
Other	11,764	11,819	6,670
Total noninterest income	143,565	145,749	140,029
Noninterest expense:
Salaries and employee benefits	234,747	233,130	194,446
Occupancy expense	47,457	49,165	40,925
Information services expense	35,477	34,322	25,462
OREO expense and loan related	3,242	3,510	6,721
Pension plan termination expense	9,526
Amortization of intangibles	13,084	14,209	10,353
Supplies, printing and postage expense	5,881	5,839	6,148
Professional fees	10,325	8,883	5,975
FDIC assessment and other regulatory charges	4,545	8,405	3,924
Advertising and marketing	4,309	4,221	3,963
Merger and branch consolidation related expense	4,552	29,868	44,503
Other	31,493	29,375	25,900
Total noninterest expense	404,638	420,927	368,320
Earnings:
Income before provision for income taxes	230,425	224,255	168,805
Provision for income taxes	43,942	45,384	81,251
Net income	$ 186,483	$ 178,871	$ 87,554
Earnings per common share:
Basic (in dollars per share)	$ 5.40	$ 4.90	$ 2.95
Diluted (in dollars per share)	$ 5.36	$ 4.86	$ 2.93
Weighted average common shares outstanding:
Basic (in shares)	34,561	36,530	29,686
Diluted (in shares)	34,797	36,776	29,922
Fees on deposit accounts
Noninterest income:
Noninterest income	$ 75,435	$ 81,649	$ 80,764
Mortgage banking income
Noninterest income:
Noninterest income	17,564	13,590	17,954
Trust and investment services income
Noninterest income:
Noninterest income	$ 29,244	$ 30,229	$ 25,401