Basis of Accounting and Consolidation - Additional Information (Details) - USD ($)					12 Months Ended
	Jul. 28, 2021	Feb. 02, 2021	Sep. 25, 2020	Jan. 02, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2020	Jan. 01, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Common stock, par value (in dollars per share)					$ 4	$ 4
Assets					$ 5,986,582,000	$ 4,726,348,000
Loans					3,938,120,000	3,094,585,000
Deposits					4,956,486,000	3,692,784,000
Loans acquired					208,000,000	$ 183,000,000
Customer deposits assumed					219,000,000
Core deposit intangible asset					$ 4,900,000
Federal funds selling period						1 day
Intangible assets amortization period					15 years
Captive maximum gross premiums					$ 2,400,000,000
Value of trust accounts					$ 5,100,000,000	$ 4,500,000,000
Stock plans, term					10 years
Maximum number of shares to be issued in stock incentive plan (in shares)					149,983
RSA/RSU, grants in period, gross					48,575	25,950	26,700
Employee discount for employee stock purchase plan					5.00%
Employee stock purchase plan, number of shares authorized					600,000
Stock issued during period, shares, employee stock purchase plans					11,748	11,037	8,899
Right of use lease assets					$ 15,116,000	$ 17,209,000
Lease liabilities					15,322,000	17,351,000
Cumulative change in accounting principal					633,894,000	568,228,000	$ 526,609,000			$ 475,864,000
Allowance for credit losses on loans					$ 54,655,000	$ 41,910,000	26,911,000			$ 26,189,000
Accounting Standards Update 2016-02
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]					true
Change in accounting principle, accounting standards update, adoption date					Jan. 01, 2019
Right of use lease assets									$ 14,100,000
Lease liabilities									$ 14,100,000
ASU 2016-13
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses on loans								$ 28,583,000
Off-balance sheet, credit loss, liability								69,000
Allowance for credit losses, held-to-maturity debt securities								0
Amortized cost of PCD assets reflected the addition to allowance for credit losses				$ 833,000,000
ASU 2016-13 | Revision of Prior Period, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses on loans								1,672,000
Off-balance sheet, credit loss, liability								69,000
ASU 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Cumulative change in accounting principal							(717,000)	$ (717,000)
Allowance for credit losses on loans							$ 1,672,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Certificates of deposit investments original maturities period					3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Certificates of deposit investments original maturities period					5 years
Delta Bancshare Company
Summary Of Significant Accounting Policies [Line Items]
Percentage of issued and outstanding shares acquired	100.00%
Common stock, par value (in dollars per share)	$ 10.00
Share Price	$ 4.00
Consideration payable in cash	$ 15,200,000
Consideration payable in shares	2,292,270
Assets					$ 718,000,000
Loans					424,000,000
Deposits					$ 560,000,000
LINCO Bancshares, Inc.
Summary Of Significant Accounting Policies [Line Items]
Percentage of issued and outstanding shares acquired			100.00%
Common stock, par value (in dollars per share)			$ 1.00
Share Price			$ 4.00
Consideration payable in cash		$ 103,500,000	$ 103,500,000
Consideration payable in shares			1,262,246
Consideration payable in shares			1,262,246
Dividends			$ 13,000,000