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v3.24.3

Segment Reporting - Summary of Gross and Net Written and Earned Premiums, Underwriting Results, Ratios and Reserves for Each of Company's Business Segments (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross written premiums | $ 1,116.8 | $ 982.7 | $ 3,598.6 | $ 3,107.9 | $ 3,967.6 | $ 4,338.7 | $ 3,938.4 |
Net written premiums | 673.6 | 628.6 | 2,225.6 | 1,979.1 | 2,581.9 | 2,896.0 | 2,587.7 |
Gross earned premiums | 1,102.2 | 1,021.2 | 3,174.4 | 2,980.5 | 4,006.8 | 3,988.0 | 3,618.3 |
Net earned premiums | 698.3 | 660.0 | 2,069.4 | 1,947.4 | 2,614.5 | 2,688.7 | 2,410.5 |
Losses and loss adjustment expenses | 474.2 | 430.5 | 1,278.9 | 1,147.6 | 1,553.0 | 1,680.0 | 1,693.3 |
Acquisition costs | 91.7 | 94.3 | 290.2 | 287.2 | 380.2 | 431.8 | 414.1 |
General and administrative expenses | 99.4 | 87.3 | 297.5 | 256.3 | 354.5 | 386.5 | 333.1 |
Underwriting income (loss) | 33.0 | 47.9 | 202.8 | 256.3 | 326.8 | 190.4 | (30.0) |
Corporate and other expenses | (18.6) | (32.6) | (83.3) | (85.7) | (114.0) | (71.7) | (64.3) |
Non-operating expenses | (7.6) | (0.2) | (19.3) | (10.8) | (35.1) | (36.0) | (20.6) |
Net investment income | 79.6 | 77.9 | 238.9 | 207.3 | 275.7 | 188.1 | 147.5 |
Realized and unrealized investment gains (losses) | 22.0 | 11.3 | 48.8 | 47.4 | 75.9 | 5.0 | 56.2 |
Realized and unrealized investment losses | (15.9) | (13.1) | (69.8) | (31.2) | (61.4) | (182.6) | (47.4) |
Change in fair value of derivatives | 37.8 | (35.6) | 22.2 | (16.0) | 26.1 | (80.5) | (35.9) |
Interest income (expense) | (20.9) | 1.8 | (51.0) | (41.1) |  |  |  |
Net realized and unrealized foreign exchange gains | (46.3) | 34.1 | (19.7) | 20.4 | (36.2) | 15.9 | 40.0 |
Income (loss) from operations before income taxes | 63.1 | 91.5 | 269.6 | 346.6 | 402.6 | (27.0) | 35.1 |
Income tax benefit/(expense) | (6.4) | (5.2) | (32.1) | (41.4) | 132.1 | 78.1 | (5.3) |
Net income/(loss) | 56.7 | 86.3 | 237.5 | 305.2 | 534.7 | 51.1 | 29.8 |
Losses and loss adjustment expenses | 8,201.3 | 7,770.8 | 8,201.3 | 7,770.8 | 7,810.6 | 7,710.9 | 7,611.8 | $ 7,165.3
Net reserves for losses and loss adjustment expenses | $ 3,770.0 | $ 3,174.1 | $ 3,770.0 | $ 3,174.1 | $ 3,232.8 | $ 2,813.2 | $ 4,313.7 | $ 3,970.1
Ratios |  |  |  |  |  |  |  |
Loss ratio | 67.90% | 65.20% | 61.80% | 58.90% | 59.40% | 62.50% | 70.20% |
Acquisition cost ratio | 13.10% | 14.30% | 14.00% | 14.70% | 14.50% | 16.10% | 17.20% |
General and administrative expense ratio | 14.20% | 13.20% | 14.40% | 13.20% | 13.60% | 14.40% | 13.80% |
Expense ratio | 27.30% | 27.50% | 28.40% | 27.90% | 28.10% | 30.50% | 31.00% |
Combined ratio | 95.20% | 92.70% | 90.20% | 86.80% | 87.50% | 93.00% | 101.20% |
Reinsurance |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Net written premiums |  |  |  |  | $ 1,098.0 | $ 1,426.4 | $ 1,199.0 |
Net earned premiums |  |  |  |  | 1,154.5 | 1,251.8 | 1,118.8 |
Losses and loss adjustment expenses | $ 1,655.0 | $ 1,404.8 | $ 1,655.0 | $ 1,404.8 | 1,373.1 | 1,360.7 | 2,148.4 |
Net reserves for losses and loss adjustment expenses |  |  |  |  | $ 1,373.1 | $ 1,360.7 | $ 2,148.4 |
Ratios |  |  |  |  |  |  |  |
Loss ratio | 71.10% | 53.00% | 59.80% | 52.30% | 52.90% | 61.50% | 63.00% |
Acquisition cost ratio | 15.00% | 18.80% | 17.10% | 18.60% | 18.10% | 20.20% | 19.80% |
General and administrative expense ratio | 14.00% | 10.20% | 12.30% | 10.20% | 10.40% | 11.40% | 10.80% |
Expense ratio | 29.00% | 29.00% | 29.40% | 28.80% | 28.50% | 31.60% | 30.60% |
Combined ratio | 100.10% | 82.00% | 89.20% | 81.10% | 81.40% | 93.10% | 93.60% |
Insurance |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Net written premiums |  |  |  |  | $ 1,483.9 | $ 1,469.6 | $ 1,388.7 |
Net earned premiums |  |  |  |  | 1,460.0 | 1,436.9 | 1,291.7 |
Losses and loss adjustment expenses | $ 2,115.0 | $ 1,769.3 | $ 2,115.0 | $ 1,769.3 | 1,859.7 | 1,452.5 | 2,165.3 |
Net reserves for losses and loss adjustment expenses |  |  |  |  | $ 1,859.7 | $ 1,452.5 | $ 2,165.3 |
Ratios |  |  |  |  |  |  |  |
Loss ratio | 65.60% | 74.90% | 63.40% | 64.20% | 64.50% | 63.30% | 76.50% |
Acquisition cost ratio | 11.80% | 10.70% | 11.50% | 11.70% | 11.80% | 12.50% | 14.90% |
General and administrative expense ratio | 14.40% | 15.60% | 16.10% | 15.50% | 16.00% | 17.00% | 16.40% |
Expense ratio | 26.20% | 26.30% | 27.60% | 27.20% | 27.80% | 29.50% | 31.30% |
Combined ratio | 91.80% | 101.20% | 91.00% | 91.40% | 92.30% | 92.80% | 107.80% |
Operating Segments | Reinsurance |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross written premiums | $ 416.2 | $ 367.5 | $ 1,596.8 | $ 1,243.2 | $ 1,521.0 | $ 1,807.0 | $ 1,597.0 |
Net written premiums | 263.7 | 261.2 | 1,052.0 | 866.2 | 1,098.0 | 1,426.4 | 1,199.0 |
Gross earned premiums | 449.7 | 403.1 | 1,298.2 | 1,158.8 | 1,562.0 | 1,617.2 | 1,479.2 |
Net earned premiums | 293.5 | 291.8 | 925.3 | 863.8 | 1,154.5 | 1,251.8 | 1,118.8 |
Losses and loss adjustment expenses | 208.6 | 154.7 | 553.0 | 451.9 | 611.1 | 770.3 | 705.2 |
Acquisition costs | 43.9 | 54.9 | 158.5 | 160.6 | 208.6 | 252.4 | 221.6 |
General and administrative expenses | 41.2 | 29.7 | 113.7 | 88.1 | 120.6 | 142.5 | 121.3 |
Underwriting income (loss) | (0.2) | 52.5 | 100.1 | 163.2 | 214.2 | 86.6 | 70.7 |
Operating Segments | Insurance |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross written premiums | 700.6 | 615.2 | 2,001.8 | 1,864.7 | 2,446.6 | 2,531.7 | 2,341.4 |
Net written premiums | 409.9 | 367.4 | 1,173.6 | 1,112.9 | 1,483.9 | 1,469.6 | 1,388.7 |
Gross earned premiums | 652.5 | 618.1 | 1,876.2 | 1,821.7 | 2,444.8 | 2,370.8 | 2,139.1 |
Net earned premiums | 404.8 | 368.2 | 1,144.1 | 1,083.6 | 1,460.0 | 1,436.9 | 1,291.7 |
Losses and loss adjustment expenses | 265.6 | 275.8 | 725.9 | 695.7 | 941.9 | 909.7 | 988.1 |
Acquisition costs | 47.8 | 39.4 | 131.7 | 126.6 | 171.6 | 179.4 | 192.5 |
General and administrative expenses | 58.2 | 57.6 | 183.8 | 168.2 | 233.9 | 244.0 | 211.8 |
Underwriting income (loss) | $ 33.2 | $ (4.6) | $ 102.7 | $ 93.1 | $ 112.6 | $ 103.8 | $ (100.7) |

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