Basis of Presentation and Summary of Significant Accounting Policies (Tables)
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6 Months Ended |
Jun. 30, 2026 |
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| Accounting Policies [Abstract] |
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| Schedule of Goodwill and Intangible Assets |
| | | | | | | | | June 30, | | December 31, | (in thousands) | | 2026 | | 2025 | Goodwill | | | | | | | Surety | | $ | 40,816 | | $ | 40,816 | Casualty | | | 5,246 | | | 5,246 | Total goodwill | | $ | 46,062 | | $ | 46,062 | Indefinite-lived intangibles | | | 7,500 | | | 7,500 | Total goodwill and intangibles | | $ | 53,562 | | $ | 53,562 |
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| Schedule of Reconciliation of Numerator and Denominator of the Basic and Diluted Earnings Per Share Computations |
| | | | | | | | | | | | | | | | | | | | | For the Three Months | | For the Three Months | | | Ended June 30, 2026 | | Ended June 30, 2025 | | | Income | | Shares | | Per Share | | Income | | Shares | | Per Share | (in thousands, except per share data) | | (Numerator) | | (Denominator) | | Amount | | (Numerator) | | (Denominator) | | Amount | Basic EPS | | | | | | | | | | | | | | | | | | | Earnings available to common shareholders | | $ | 168,028 | | | 91,922 | | $ | 1.83 | | $ | 124,336 | | | 91,827 | | $ | 1.35 | Effect of Dilutive Securities | | | | | | | | | | | | | | | | | | | Stock options and restricted stock units | | | — | | | 238 | | | | | | — | | | 691 | | | | Diluted EPS | | | | | | | | | | | | | | | | | | | Earnings available to common shareholders | | $ | 168,028 | | | 92,160 | | $ | 1.82 | | $ | 124,336 | | | 92,518 | | $ | 1.34 | Anti-dilutive securities excluded from diluted EPS | | | | | | 1,150 | | | | | | | | | 48 | | | | | | | | | | | | | | | | | | | | | | | | | For the Six Months | | For the Six Months | | | Ended June 30, 2026 | | Ended June 30, 2025 | | | Income | | Shares | | Per Share | | Income | | Shares | | Per Share | (in thousands, except per share data) | | (Numerator) | | (Denominator) | | Amount | | (Numerator) | | (Denominator) | | Amount | Basic EPS | | | | | | | | | | | | | | | | | | | Earnings available to common shareholders | | $ | 222,913 | | | 91,924 | | $ | 2.42 | | $ | 187,550 | | | 91,799 | | $ | 2.04 | Effect of Dilutive Securities | | | | | | | | | | | | | | | | | | | Stock options and restricted stock units | | | — | | | 333 | | | | | | — | | | 713 | | | | Diluted EPS | | | | | | | | | | | | | | | | | | | Earnings available to common shareholders | | $ | 222,913 | | | 92,257 | | $ | 2.42 | | $ | 187,550 | | | 92,512 | | $ | 2.03 | Anti-dilutive securities excluded from diluted EPS | | | | | | 1,062 | | | | | | | | | 48 | | | |
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| Schedule of Changes in the Balance of Each Component of Accumulated Other Comprehensive Earnings (Loss) |
| | | | | | | | | | | | | (in thousands) | | For the Three Months | | For the Six Months | | | Ended June 30, | | Ended June 30, | Unrealized Gains (Losses) on Available-for-Sale Securities | | 2026 | | 2025 | | 2026 | | 2025 | Beginning balance | | $ | (113,440) | | $ | (143,693) | | $ | (88,074) | | $ | (173,723) | Other comprehensive earnings (loss) before reclassifications | | | (2,655) | | | 17,922 | | | (28,632) | | | 47,822 | Amounts reclassified from accumulated other comprehensive earnings | | | 341 | | | 779 | | | 952 | | | 909 | Net current-period other comprehensive earnings (loss) | | $ | (2,314) | | $ | 18,701 | | $ | (27,680) | | $ | 48,731 | Ending balance | | $ | (115,754) | | $ | (124,992) | | $ | (115,754) | | $ | (124,992) | Balance of securities for which an allowance for credit losses has been recognized in net earnings | | | | | | | | $ | 1,465 | | $ | 1,102 |
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| Schedule of Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Loss) |
| | | | | | | | | | | | | | | | | | Amount Reclassified from Accumulated Other | | | | (in thousands) | | Comprehensive Earnings (Loss) | | | | | | For the Three Months | | For the Six Months | | | | Component of Accumulated | | Ended June 30, | | Ended June 30, | | | Affected line item in the | Other Comprehensive Earnings (Loss) | | 2026 | | 2025 | | 2026 | | 2025 | | | Statement of Earnings | Unrealized gains and losses on available-for-sale securities | | $ | (507) | | $ | (898) | | $ | (1,570) | | $ | (1,103) | | | Net realized gains (losses) | | | | 75 | | | (88) | | | 365 | | | (48) | | | Credit gains (losses) presented within net realized gains | | | $ | (432) | | $ | (986) | | $ | (1,205) | | $ | (1,151) | | | Earnings (loss) before income taxes | | | | 91 | | | 207 | | | 253 | | | 242 | | | Income tax (expense) benefit | | | $ | (341) | | $ | (779) | | $ | (952) | | $ | (909) | | | Net earnings (loss) |
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