| Reconciliation of Components Used to Derive Basic and Diluted EPS | The following table is a reconciliation of the components used to derive basic and diluted EPS for the periods indicated:   
       
        |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
        |   |   | Three Months Ended |   |   | Nine Months Ended |   |  
        |   |   | September 30, |   |   | September 30, |   |  
        |   |   | 2023 |   |   | 2022 |   |   | 2023 |   |   | 2022 |   |  
        |   |   | (dollars in thousands, except per share amounts) |   |  
        | Basic EPS |   |   |   |   |   |   |   |   |   |   |   |   |  
        | Net income |   | $ | 18,796 |   |   | $ | 27,169 |   |   | $ | 61,408 |   |   | $ | 72,915 |   |  
        | Less: income allocated to unvested restricted stock |   |   | 117 |   |   |   | 163 |   |   |   | 381 |   |   |   | 408 |   |  
        | Income allocated to common shares |   | $ | 18,679 |   |   | $ | 27,006 |   |   | $ | 61,027 |   |   | $ | 72,507 |   |  
        | Weighted-average shares for basic EPS |   |   | 30,251,961 |   |   |   | 30,314,439 |   |   |   | 30,296,991 |   |   |   | 30,289,068 |   |  
        | Basic EPS (1) |   | $ | 0.62 |   |   | $ | 0.89 |   |   | $ | 2.01 |   |   | $ | 2.39 |   |  
        |   |   |   |   |   |   |   |   |   |   |   |   |   |  
        | Effect of dilutive stock options and unvested performance stock units |   |   | 40,910 |   |   |   | 82,323 |   |   |   | 41,686 |   |   |   | 80,470 |   |  
        |   |   |   |   |   |   |   |   |   |   |   |   |   |  
        | Diluted EPS |   |   |   |   |   |   |   |   |   |   |   |   |  
        | Income allocated to common shares |   | $ | 18,679 |   |   | $ | 27,006 |   |   | $ | 61,027 |   |   | $ | 72,507 |   |  
        | Weighted-average shares for diluted EPS |   |   | 30,292,872 |   |   |   | 30,396,762 |   |   |   | 30,338,678 |   |   |   | 30,369,538 |   |  
        | Diluted EPS (1) |   | $ | 0.62 |   |   | $ | 0.89 |   |   | $ | 2.01 |   |   | $ | 2.39 |   |    
(1)Per share amounts may not be able to be recalculated using net income and weighted-average shares presented above due to rounding. |