Consolidated Statements of Earnings (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
INTEREST INCOME:
Interest and fees on loans	$ 51,428	$ 42,749	$ 147,279	$ 123,643
Interest on investment securities:
Taxable	12,593	8,074	36,666	23,848
Exempt from federal income tax	9,558	11,091	29,882	33,991
Interest on federal funds sold and interest-bearing deposits in banks	470	640	1,382	1,037
Total interest income	74,049	62,554	215,209	182,519
INTEREST EXPENSE:
Interest on deposits	4,330	2,228	11,854	5,748
Other	293	638	869	978
Total interest expense	4,623	2,866	12,723	6,726
Net interest income	69,426	59,688	202,486	175,793
PROVISION FOR LOAN LOSSES	1,450	1,415	3,865	5,090
Net interest income after provision for loan losses	67,976	58,273	198,621	170,703
NONINTEREST INCOME:
ATM, interchange and credit card fees	7,533	6,340	21,570	19,102
Net gain on sale of available-for-sale securities (includes $58 and $1,075 for the three months ended September 30, 2018 and 2017, respectively, and $1,346 and $1,825 for the nine months ended September 30, 2018 and 2017, respectively, related to accumulated other comprehensive earnings reclassifications)	58	1,075	1,346	1,825
Net gain (loss) on sale of foreclosed assets	84	(11)	201	(42)
Net gain (loss) on sale of assets	(61)	(15)	(152)	(211)
Interest on loan recoveries	199	405	607	896
Other	1,427	1,452	4,461	3,328
Total noninterest income	27,055	24,260	76,966	68,715
NONINTEREST EXPENSE:
Salaries and employee benefits	26,377	24,143	79,442	70,867
Net occupancy expense	2,900	2,711	8,589	8,081
Equipment expense	3,482	3,294	10,438	10,397
FDIC insurance premiums	570	561	1,768	1,657
ATM, interchange and credit card expenses	2,344	2,001	6,692	5,517
Professional and service fees	2,174	2,036	6,613	5,878
Printing, stationery and supplies	387	449	1,485	1,423
Operational and other losses	981	1,081	1,852	2,639
Software amortization and expense	540	742	1,542	2,237
Amortization of intangible assets	279	143	1,049	477
Other	7,472	6,803	22,978	20,718
Total noninterest expense	47,506	43,964	142,448	129,891
EARNINGS BEFORE INCOME TAXES	47,525	38,569	133,139	109,527
INCOME TAX EXPENSE (includes $12 and $376 for the three months ended September 30, 2018 and 2017, respectively, and $283 and $639 for the nine months ended September 30, 2018 and 2017, respectively, related to income tax expense from reclassification items)	7,475	9,195	20,937	25,300
NET EARNINGS	$ 40,050	$ 29,374	$ 112,202	$ 84,227
EARNINGS PER SHARE, BASIC	$ 0.59	$ 0.44	$ 1.66	$ 1.27
EARNINGS PER SHARE, ASSUMING DILUTION	0.59	0.44	1.65	1.27
DIVIDENDS PER SHARE	$ 0.21	$ 0.19	$ 0.61	$ 0.56
Trust Fees [Member]
NONINTEREST INCOME:
Revenue from contract with customer	$ 7,291	$ 6,040	$ 21,265	$ 17,804
Service Charges on Deposit Accounts [Member]
NONINTEREST INCOME:
Revenue from contract with customer	5,690	5,083	15,950	14,517
Real Estate Mortgage Operations [Member]
NONINTEREST INCOME:
Revenue from contract with customer	$ 4,834	$ 3,891	$ 11,718	$ 11,496