Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income:
Loans and leases, including fees	$ 377,402	$ 397,628	$ 293,284
Investment securities:
Investment securities available-for-sale	36,052	39,330	45,988
Investment securities held-to-maturity	14,223	17,388	18,901
Total investment income	50,275	56,718	64,889
Dividends from FHLB stock	978	1,235	2,045
Interest-earning deposits with other institutions	1,682	2,269	1,642
Total interest income	430,337	457,850	361,860
Interest expense:
Deposits	12,602	17,120	9,825
Borrowings and customer repurchase agreements	1,131	3,959	2,067
Junior subordinated debentures	551	999	923
Total interest expense	14,284	22,078	12,815
Net interest income before provision for credit losses	416,053	435,772	349,045
Provision for credit losses	23,500	5,000	1,500
Net interest income after provision for credit losses	392,553	430,772	347,545
Noninterest income:
BOLI income	8,100	5,798	4,018
Gain on OREO, net	388	129	3,546
Gain on sale of building, net	1,680	4,776	0
Gain on eminent domain condemnation, net	0	5,685	0
Other	11,277	9,956	6,588
Total noninterest income	49,870	59,042	43,481
Noninterest expense:
Salaries and employee benefits	119,759	119,475	100,601
Occupancy and equipment	20,622	20,457	20,153
Professional services	9,460	7,752	6,477
Computer software expense	11,302	10,658	9,343
Marketing and promotion	4,488	5,890	5,302
Recapture of provision for unfunded loan commitments	0	0	(250)
Amortization of intangible assets	9,352	10,798	5,254
Acquisition related expenses	0	6,447	16,404
Other	17,920	17,263	16,627
Total noninterest expense	192,903	198,740	179,911
Earnings before income taxes	249,520	291,074	211,115
Income taxes	72,361	83,247	59,112
Net earnings	177,159	207,827	152,003
Other comprehensive income (loss):
Unrealized gain (loss) on securities arising during the period, before tax	32,277	43,872	(28,526)
Less: Reclassification adjustment for net gain on securities included in net income	0	(5)	0
Other comprehensive income (loss), before tax	32,277	43,867	(28,526)
Less: Income tax (expense) benefit related to items of other comprehensive income	(9,542)	(12,969)	8,434
Other comprehensive income (loss), net of tax	22,735	30,898	(20,092)
Comprehensive income	$ 199,894	$ 238,725	$ 131,911
Basic earnings per common share	$ 1.30	$ 1.48	$ 1.25
Diluted earnings per common share	$ 1.30	$ 1.48	$ 1.24
Service Charges on Deposit Accounts [Member]
Noninterest income:
Revenue from contract with customer, including assessed tax	$ 16,561	$ 20,010	$ 17,070
Trust and Investment Services [Member]
Noninterest income:
Revenue from contract with customer, including assessed tax	9,978	9,525	8,774
Bankcard Services [Member]
Noninterest income:
Revenue from contract with customer, including assessed tax	$ 1,886	$ 3,163	$ 3,485