Consolidated Statement of Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTEREST INCOME:
Interest and fees on loans	$ 166,807	$ 161,018	$ 151,662
Interest on investment securities:
Taxable	32,825	27,626	29,673
Exempt from federal income tax	44,659	43,302	40,080
Interest on federal funds sold and interest-bearing deposits in banks	1,684	342	208
Total interest income	245,975	232,288	221,623
INTEREST EXPENSE:
Interest on deposits	8,213	4,503	3,642
Other	1,075	948	446
Total interest expense	9,288	5,451	4,088
Net interest income	236,687	226,837	217,535
PROVISION FOR LOAN LOSSES	6,530	10,212	9,685
Net interest income after provision for loan losses	230,157	216,625	207,850
NONINTEREST INCOME:
Trust fees	23,694	19,636	19,252
Service charges on deposit accounts	19,416	18,386	17,171
ATM, interchange and credit card fees	25,686	23,910	21,860
Real estate mortgage operations	15,109	16,086	10,409
Net gain on sale of available-for-sale securities (includes $1,828, $1,270 and $432 for the years ended December 31, 2017, 2016 and 2015, respectively, related to accumulated comprehensive earnings reclassifications)	1,828	1,270	432
Net gain (loss) on sale of foreclosed assets	(50)	456	538
Net gain (loss) on sale of assets	(396)	168	(820)
Interest on loan recoveries	1,128	2,112	1,050
Other	4,602	3,108	3,540
Total noninterest income	91,017	85,132	73,432
NONINTEREST EXPENSE:
Salaries and employee benefits	95,287	90,739	80,999
Loss from partial settlement of pension plan		267
Net occupancy expense	10,521	10,420	10,314
Equipment expense	13,765	13,479	12,222
FDIC insurance premiums	2,217	2,680	3,153
ATM, interchange and credit card expenses	7,452	7,231	6,384
Professional and service fees	8,063	6,877	4,831
Printing, stationery and supplies	1,989	2,093	2,278
Operational and other losses	3,192	2,170	1,889
Amortization of intangible assets	613	738	561
Other	30,887	29,136	26,833
Total noninterest expense	173,986	165,830	149,464
EARNINGS BEFORE INCOME TAXES	147,188	135,927	131,818
INCOME TAX EXPENSE (includes $640, $445 and $151 for the years ended December 31, 2017, 2016 and 2015, respectively, related to income tax expense from reclassification items)	26,817	31,153	31,437
NET EARNINGS	$ 120,371	$ 104,774	$ 100,381
NET EARNINGS PER SHARE, BASIC	$ 1.82	$ 1.59	$ 1.55
NET EARNINGS PER SHARE, ASSUMING DILUTION	$ 1.81	$ 1.59	$ 1.54