Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Interest income:
Loans, including fees	$ 134,953	$ 132,043	$ 402,175	$ 388,936
Investment securities:
Taxable	10,785	8,890	28,933	26,726
Tax-exempt	1,587	1,521	4,700	4,695
Federal funds sold and securities purchased under agreements to resell	2,676	1,106	7,565	2,983
Total interest income	150,001	143,560	443,373	423,340
Interest expense:
Deposits	16,655	13,220	50,693	30,142
Federal funds purchased and securities sold under agreements to repurchase	612	599	2,037	1,696
Other borrowings	5,361	1,452	12,824	4,678
Total interest expense	22,628	15,271	65,554	36,516
Net interest income	127,373	128,289	377,819	386,824
Provision for loan losses	4,028	3,117	9,220	10,049
Net interest income after provision for loan losses	123,345	125,172	368,599	376,775
Noninterest income:
Securities gains (losses), net	437	(11)	2,687	(652)
Recoveries on acquired loans	1,401	1,238	4,615	6,379
Other	2,584	2,659	7,566	7,738
Total noninterest income	37,582	32,027	107,258	110,107
Noninterest expense:
Salaries and employee benefits	59,551	57,934	176,529	175,425
Occupancy expense	11,883	12,235	35,344	37,361
Information services expense	8,878	7,804	26,558	26,445
OREO expense and loan related	597	(19)	2,229	2,679
Pension plan termination expense			9,526
Amortization of intangibles	3,268	3,537	9,817	10,672
Supplies, printing and postage expense	1,418	1,561	4,417	4,359
Professional fees	2,442	2,138	7,463	5,735
FDIC assessment and other regulatory charges	228	2,525	3,218	7,065
Advertising and marketing	1,052	1,049	2,818	2,948
Merger and branch consolidation related expense		4,476	3,058	29,868
Other	7,047	7,054	23,033	21,706
Total noninterest expense	96,364	100,294	304,010	324,263
Earnings:
Income before provision for income taxes	64,563	56,905	171,847	162,619
Provision for income taxes	12,998	9,823	34,455	32,752
Net income	$ 51,565	$ 47,082	$ 137,392	$ 129,867
Earnings per common share:
Basic (in dollars per share)	$ 1.51	$ 1.28	$ 3.94	$ 3.53
Diluted (in dollars per share)	$ 1.50	$ 1.28	$ 3.92	$ 3.52
Weighted average common shares outstanding:
Basic (in shares)	34,057	36,645	34,859	36,657
Diluted (in shares)	34,300	36,893	35,069	36,909
Fees on deposit accounts
Noninterest income:
Noninterest income	$ 19,725	$ 17,790	$ 56,274	$ 62,945
Mortgage banking income
Noninterest income:
Noninterest income	6,115	2,824	13,807	11,089
Trust and investment services income
Noninterest income:
Noninterest income	$ 7,320	$ 7,527	$ 22,309	$ 22,608