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EMPLOYEE BENEFITS AND STOCK BASED COMPENSATION (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2022
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 plans described above, in 2022, 2021, and 2020 (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2022 |  | 2021 |  | 2020
401(k) Plan | ​ | $ | 7,037 | ​ | $ | 6,515 | ​ | $ | 6,265
ESOP | ​ |  | 750 | ​ |  | 750 | ​ |  | 1,000
Cash | ​ |  | 667 | ​ |  | 674 | ​ |  | 697
Total | ​ | $ | 8,454 | ​ | $ | 7,939 | ​ | $ | 7,962
​
Schedule of Recognized Stock-Based Compensation Expense | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
​ |  | 2022 |  | 2021 |  | 2020
Stock-based compensation expense | ​ | $ | 10,609 | ​ | $ | 10,091 | ​ | $ | 9,258
Reduction of income tax expense | ​ |  | 2,228 | ​ |  | 2,119 | ​ |  | 1,944
Per share compensation cost | ​ | $ | 0.11 | ​ | $ | 0.10 | ​ | $ | 0.09
​
Summary of Stock Option Activity | The following table summarizes the stock option activity during the year ended December 31, 2022:
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | ​ | ​ |  | Weighted |  | ​ | ​
​ | ​ | ​ | ​ | Weighted | ​ | Average | ​ | ​ | ​
​ | ​ | Stock | ​ | Average | ​ | Remaining | ​ | Aggregate
​ | ​ | Options | ​ | Exercise | ​ | Contractual | ​ | Intrinsic
​ | ​ | (shares) | ​ | Price | ​ | Life | ​ | Value
Outstanding as of December 31, 2021 |  | 208,755 | ​ | $ | 35.43 |  |  |  | ​ |
Granted |  | — | ​ |  | — |  |  |  | ​ |
Exercised |  | (111,774) | ​ |  | 34.56 |  |  |  | ​ |
Forfeited |  | (1,512) | ​ |  | 31.83 |  |  |  | ​ |
Expired |  | (12,102) | ​ |  | 37.70 |  |  |  | ​ |
Outstanding as of December 31, 2022 |  | 83,367 | ​ |  | 36.32 |  | 0.57 | ​ | $ | 105,665
Exercisable as of December 31, 2022 |  | 76,693 | ​ |  | 36.71 |  | 0.52 | ​ |  | 83,574
​
Summary of Nonvested Stock Activity | ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Weighted
​ | ​ | Number of | ​ | Average
​ | ​ | Shares of | ​ | Grant-Date Fair
​ | ​ | RSAs | ​ | Value
Unvested as of December 31, 2021 |  | 400,067 | ​ | $ | 36.55
Granted |  | 273,010 | ​ |  | 37.99
Net settle for taxes |  | (69,025) | ​ |  | 36.56
Vested |  | (202,311) | ​ |  | 36.29
Forfeited |  | (29,635) | ​ |  | 37.90
Unvested as of December 31, 2022 |  | 372,106 | ​ |  | 37.63
​
Summary of Performance Stock Activity | ​
​ | ​ | ​ | ​ | ​ | ​
​ |  | Number of |  | Weighted Average
​ | ​ | Shares of | ​ | Grant-
​ | ​ | PSUs | ​ | Date Fair Value
Unvested as of December 31, 2021 |  | 229,355 | ​ | $ | 33.89
Granted |  | 82,754 | ​ |  | 41.92
Net settle for taxes |  | (13,492) | ​ |  | 36.16
Vested |  | (41,374) | ​ |  | 36.16
Forfeited |  | (26,802) | ​ |  | 37.09
Unvested as of December 31, 2022 |  | 230,441 | ​ |  | 35.86
​
Schedule of Performance Stock Units Valuation Assumptions | During years ended December 31, 2022, 2021 and 2020 PSUs were awarded with a market-based component based on relative total shareholder return. The fair value of each PSU granted is estimated using the Monte Carlo simulation lattice model that uses the assumptions noted in the following table: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | 2022 |  | 2021 |  | 2020 |
Dividend yield(1) |  | 3.95 | % | 2.66 | % | 2.83 | %
Expected life in years(2) |  | 2.25 |  | 2.85 |  | 2.86 | ​
Expected volatility(3) |  | 36.32 | % | 45.75 | % | 24.33 | %
Risk-free interest rate(4) |  | 4.18 | % | 0.20 | % | 1.35 | %
(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, 2022 that will be recognized in future periods is as follows (dollars in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Restricted |  | Performance | ​ | ​ | Stock |  | ​ | ​
​ | ​ | Stock | ​ | Stock | ​ | ​ | Options | ​ | Total
2023 | ​ | $ | 5,303 | ​ | $ | 1,853 | ​ | $ | 2,766 | ​ | $ | 9,922
2024 | ​ |  | 3,155 | ​ |  | 1,060 | ​ | ​ | — | ​ |  | 4,215
2025 | ​ |  | 618 | ​ |  | — | ​ | ​ | — | ​ |  | 618
2026 | ​ |  | 9 | ​ |  | — | ​ | ​ | — | ​ |  | 9
Total | ​ | $ | 9,085 | ​ | $ | 2,913 | ​ | $ | 2,766 | ​ | $ | 14,764

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