Basis of Accounting and Consolidation - Additional Information (Details)				3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 28, 2021 USD ($) $ / shares shares	Oct. 06, 2020 USD ($)	Jan. 02, 2020 USD ($)	Jun. 30, 2021 USD ($) Lender Personnel $ / shares shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2021 USD ($) Lender Personnel $ / shares shares	Jun. 30, 2020 USD ($) shares	Dec. 31, 2020 USD ($) $ / shares shares	Mar. 31, 2021 USD ($)	Apr. 21, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Basis Of Accounting And Consolidation [Line Items]
Common stock, par value (in dollars per share) | $ / shares				$ 4		$ 4		$ 4
Assets				$ 5,790,582,000		$ 5,790,582,000		$ 4,726,348,000
Loans				3,738,840,000		3,738,840,000		3,094,585,000
Deposits				4,739,322,000		4,739,322,000		3,692,784,000
Loans to be acquired				225,000,000		225,000,000
Deposits to be acquired				$ 280,000,000		$ 280,000,000
Number of commercial lenders to be acquired | Lender				4		4
Number of support personnel to be acquired | Personnel				2		2
Loans acquired										$ 183,000,000
Stock plans, term						10 years
Maximum number of shares to be issued in stock incentive plan (in shares) | shares				399,983		399,983
Employee discount for employee stock purchase plan						5.00%
Employee stock purchase plan, number of shares authorized | shares				600,000		600,000
Stock issued during period, shares, employee stock purchase plans | shares				2,597	3,739	8,439	7,543
Captive maximum gross premiums						$ 2,300,000
Cumulative change in accounting principal				$ 616,066,000	$ 549,273,000	616,066,000	$ 549,273,000	568,228,000	$ 601,884,000		$ 533,051,000		$ 526,609,000
Allowance for credit losses on loans				54,597,000	$ 38,381,000	$ 54,597,000	$ 38,381,000	$ 41,910,000	$ 55,418,000		$ 32,876,000		26,911,000
ASU 2016-13
Basis Of Accounting And Consolidation [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
ASU 2016-13 | Impact of ASU
Basis Of Accounting And Consolidation [Line Items]
Allowance for credit losses on loans												1,672,000
Off-balance sheet, credit loss, liability												69,000
Cumulative Effect, Period of Adoption, Adjustment | ASU 2016-13
Basis Of Accounting And Consolidation [Line Items]
Cumulative change in accounting principal												$ 717,000	(717,000)
Allowance for credit losses on loans													$ 1,672,000
Stock Options
Basis Of Accounting And Consolidation [Line Items]
Common stock awarded in SI plan (in shares) | shares						0
Restricted Stock
Basis Of Accounting And Consolidation [Line Items]
Common stock awarded in SI plan (in shares) | shares						27,750		25,200
Restricted Stock Units (RSUs)
Basis Of Accounting And Consolidation [Line Items]
Common stock awarded in SI plan (in shares) | shares						35,400		16,950
3.95% Subordinated Notes due 2030
Basis Of Accounting And Consolidation [Line Items]
Aggregate principal amount		$ 96,000,000.0
Fixed-to-Floating Rate		3.95%
Maturity date		Oct. 15, 2030
Redemption description		The Company may, beginning with the interest payment date of October 15, 2025, and on any interest payment date thereafter, redeem the Notes, in whole or in part, at a redemption price equal to 100% of the principal amount of the Notes to be redeemed plus accrued and unpaid interest to but excluding the date of redemption. The Company may also redeem the Notes at any time, including prior to October 15, 2025, at the Company’s option, in whole but not in part, if: (i) a change or prospective change in law occurs that could prevent the Company from deducting interest payable on the Notes for U.S. federal income tax purposes; (ii) a subsequent event occurs that could preclude the Notes from being recognized as Tier 2 capital for regulatory capital purposes; or (iii) the Company is required to register as an investment company under the Investment Company Act of 1940, as amended; in each case, at a redemption price equal to 100% of the principal amount of the Notes plus any accrued and unpaid interest to but excluding the redemption date.
3.95% Subordinated Notes due 2030 | SOFR
Basis Of Accounting And Consolidation [Line Items]
Description floating rate basis		three-month Term SOFR
Basis points		3.83%
Delta Bancshares Company
Basis Of Accounting And Consolidation [Line Items]
Assets				697,000,000		$ 697,000,000
Loans				484,000,000		484,000,000
Deposits				$ 546,000,000		$ 546,000,000
Delta Bancshares Company | Subsequent Event
Basis Of Accounting And Consolidation [Line Items]
Percentage of issued and outstanding shares acquired	100.00%
Common stock, par value (in dollars per share) | $ / shares	$ 10.00
Share Price | $ / shares	$ 4.00
Consideration payable in cash	$ 15,200,000
Consideration payable in shares | shares	2,282,511