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EMPLOYEE BENEFITS AND STOCK BASED COMPENSATION (Tables) | 12 Months Ended
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Dec. 31, 2023
Employee Benefits and Share-based Compensation, Noncash [Abstract] |
Payment Made for Employee Benefit Plans | The following 401(k) Plan match and other discretionary contributions were made to the Company’s employees, in accordance with the descriptions above for the years ended December 31, (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2023 |  | 2022 |  | 2021
401(k) Plan Company Match | ​ | $ | 7,091 | ​ | $ | 7,037 | ​ | $ | 6,515
401(k) Plan ESOP Source Contribution | ​ |  | 804 | ​ |  | 750 | ​ |  | 750
Cash | ​ |  | 696 | ​ |  | 667 | ​ |  | 674
Total | ​ | $ | 8,591 | ​ | $ | 8,454 | ​ | $ | 7,939
Schedule of Recognized Stock-Based Compensation Expense | The Company recognized stock-based compensation expense, which is included in “Salaries and benefits” expense on the Company’s Consolidated Statements of Income as follows for the years ended December 31, (dollars in thousands, except per share data): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
​ |  | 2023 |  | 2022 |  | 2021
Stock-based compensation expense | ​ | $ | 11,101 | ​ | $ | 10,609 | ​ | $ | 10,091
Reduction of income tax expense | ​ |  | 2,331 | ​ |  | 2,228 | ​ |  | 2,119
Per share compensation cost | ​ | $ | 0.12 | ​ | $ | 0.11 | ​ | $ | 0.10
Summary of Stock Option Activity | The following table summarizes the stock option activity during the year ended December 31, 2023:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted |  | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | Average | ​ | ​ | ​
​ | ​ | Stock | ​ | Average | ​ | Remaining | ​ | Aggregate
​ | ​ | Options | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
​ | ​ | (shares) | ​ | Price | ​ | Life | ​ | Value
Outstanding as of December 31, 2022 |  | 83,367 | ​ | $ | 36.32 |  | 0.57 |  | $ | 105,665
Granted |  | — | ​ |  | — |  |  |  | ​ |
Exercised |  | (23,796) | ​ |  | 32.67 |  |  |  | ​ |
Forfeited |  | — | ​ |  | — |  |  |  | ​ |
Expired |  | (48,578) | ​ |  | 39.13 |  |  |  | ​ |
Outstanding as of December 31, 2023 |  | 10,993 | ​ |  | 31.83 |  | 0.06 | ​ | ​ | 51,777
Exercisable as of December 31, 2023 |  | 10,993 | ​ |  | 31.83 |  | 0.06 | ​ |  | 51,777
Summary of Restricted Stock Activity | The following table summarizes the restricted stock activity for the year ended December 31, 2023:
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted
​ | ​ | Number of | ​ | Average
​ | ​ | Shares of | ​ | Grant-Date Fair
​ | ​ | RSAs | ​ | Value
Unvested as of December 31, 2022 |  | 372,106 | ​ | $ | 37.63
Granted |  | 349,224 | ​ |  | 36.11
Net settle for taxes |  | (59,264) | ​ |  | 37.25
Vested |  | (154,741) | ​ |  | 36.20
Forfeited |  | (30,695) | ​ |  | 37.68
Unvested as of December 31, 2023 |  | 476,630 | ​ |  | 37.03
Summary of Performance Stock Activity | The Plan permits the granting of PSUs. PSUs are granted to certain employees at no cost to the recipient and are subject to vesting based on achieving certain performance metrics. Outstanding PSUs may be paid in cash or shares of common stock or a combination thereof. Holders of PSUs have no right to vote the shares represented by the units until vested. In 2023, there were two performance measures underlying the PSUs awarded, each weighted at 50%, as follows: (1) relative total shareholder return compared to the other companies comprising the KBW NASDAQ Regional Banking Index, which is a market-based condition; and (2) relative return on average tangible common equity, which is a performance-based condition. ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | Number of |  | Weighted Average
​ | ​ | Shares of | ​ | Grant-
​ | ​ | PSUs | ​ | Date Fair Value
Unvested as of December 31, 2022 |  | 230,441 | ​ | $ | 35.86
Granted |  | 91,152 | ​ |  | 36.82
Net settle for taxes |  | (9,088) | ​ |  | 32.50
Vested |  | (27,644) | ​ |  | 32.50
Forfeited |  | (55,599) | ​ |  | 33.73
Unvested as of December 31, 2023(1) |  | 229,262 | ​ |  | 37.29
(1) The number of PSUs with a performance-based condition is presented based on achieving the performance measure at the target level of performance.
Schedule of Performance Stock Units Valuation Assumptions | During the year ended December 31, 2023, the fair value of PSUs with a performance-based condition was equal to the closing sale price of the Company’s common stock on the grant date. During the years ended December 31, 2023, 2022 and 2021, the fair value of PSUs with a market-based condition was estimated using the Monte Carlo simulation lattice model that uses the assumptions noted in the following table as of December 31,: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2023 |  | 2022 |  | 2021 |
Dividend yield(1) |  | 3.19 | % | 3.95 | % | 2.66 | %
Expected life in years(2) |  | 2.85 |  | 2.25 |  | 2.85 | ​
Expected volatility(3) |  | 40.39 | % | 36.32 | % | 45.75 | %
Risk-free interest rate(4) |  | 4.39 | % | 4.18 | % | 0.20 | %
(1) Calculated as the ratio of the current dividend paid per the stock price on the date of grant. (2) Represents the remaining performance period as of the grant date. (3) Based on the historical volatility for the period commensurate with the expected life of the PSUs. (4) Based upon the zero-coupon U.S. Treasury rate commensurate with the expected life of the PSUs on the grant date.
Estimated Unamortized Compensation Expense Recognized in Future | ​ The estimated unamortized compensation expense, net of estimated forfeitures, related to, restricted stock, performance stock and stock options issued and outstanding as of December 31, 2023 that will be recognized in future periods is as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Restricted |  | Performance | ​ | ​ | Stock |  | ​ | ​
​ | ​ | Stock | ​ | Stock | ​ | ​ | Options | ​ | Total
2024 | ​ | $ | 6,911 | ​ | $ | 2,094 | ​ | $ | — | ​ | $ | 9,005
2025 | ​ |  | 4,031 | ​ |  | 1,110 | ​ | ​ | — | ​ |  | 5,141
2026 | ​ |  | 626 | ​ |  | — | ​ | ​ | — | ​ |  | 626
2027 | ​ |  | 32 | ​ |  | — | ​ | ​ | — | ​ |  | 32
Total | ​ | $ | 11,600 | ​ | $ | 3,204 | ​ | $ | — | ​ | $ | 14,804
​

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