SEGMENT INFORMATION (Details) |
3 Months Ended | 6 Months Ended | ||
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Jun. 30, 2026
USD ($)
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Jun. 30, 2025
USD ($)
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Jun. 30, 2026
USD ($)
segment
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Jun. 30, 2025
USD ($)
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| Segment Reporting [Abstract] | ||||
| Number of reportable segments | segment | 2 | |||
| Segment Information [Line Items] | ||||
| Net premiums earned | $ 1,518,984,000 | $ 1,393,431,000 | $ 2,999,451,000 | $ 2,734,251,000 |
| Other insurance related income | 5,601,000 | 8,662,000 | 11,249,000 | 12,240,000 |
| Current accident year net losses and loss expenses | (1,833,311,000) | (1,625,845,000) | ||
| Net favorable prior year reserve development | 14,836,000 | 20,229,000 | 32,899,000 | 38,166,000 |
| Acquisition costs | (316,268,000) | (275,897,000) | (620,524,000) | (540,477,000) |
| Underwriting-related general and administrative expenses | (164,889,000) | (161,078,000) | (323,046,000) | (320,241,000) |
| Net investment income | 181,594,000 | 187,297,000 | 366,333,000 | 395,009,000 |
| Net investment gains | 46,735,000 | 43,468,000 | 19,514,000 | 13,462,000 |
| Foreign exchange (losses) gains | 2,344,000 | (94,885,000) | 38,539,000 | (151,920,000) |
| Interest expense and financing costs | (16,838,000) | (16,586,000) | (33,265,000) | (33,158,000) |
| Reorganization expenses | (5,546,000) | 0 | (28,715,000) | 0 |
| Amortization of intangible assets | (2,396,000) | (2,396,000) | (4,792,000) | (5,125,000) |
| Income before income taxes and interest in income (loss) of equity method investments | 316,191,000 | 280,262,000 | 624,332,000 | 516,362,000 |
| Income tax expense | (61,404,000) | (56,199,000) | (117,211,000) | (100,521,000) |
| Interest in income (loss) of equity method investments | 3,308,000 | (705,000) | 5,738,000 | 1,586,000 |
| Net income | 258,095,000 | 223,358,000 | 512,859,000 | 417,427,000 |
| Preferred share dividends | 7,563,000 | 7,563,000 | 15,125,000 | 15,125,000 |
| Net income available to common shareholders | 250,532,000 | 215,795,000 | 497,734,000 | 402,302,000 |
| Insurance | ||||
| Segment Information [Line Items] | ||||
| Net favorable prior year reserve development | 11,852,000 | 15,216,000 | 26,911,000 | 29,194,000 |
| Reinsurance | ||||
| Segment Information [Line Items] | ||||
| Net favorable prior year reserve development | 2,984,000 | 5,013,000 | 5,988,000 | 8,972,000 |
| Operating Segments | ||||
| Segment Information [Line Items] | ||||
| Gross premiums written | 2,667,631,000 | 2,515,971,000 | 5,765,597,000 | 5,310,622,000 |
| Net premiums written | 1,605,798,000 | 1,635,434,000 | 3,512,833,000 | 3,385,473,000 |
| Net premiums earned | 1,518,984,000 | 1,393,431,000 | 2,999,451,000 | 2,734,251,000 |
| Other insurance related income | 5,601,000 | 8,662,000 | 11,249,000 | 12,240,000 |
| Current accident year net losses and loss expenses | (947,966,000) | (821,983,000) | (1,833,311,000) | (1,625,845,000) |
| Net favorable prior year reserve development | 14,836,000 | 20,229,000 | 32,899,000 | 38,166,000 |
| Acquisition costs | (316,268,000) | (275,897,000) | (620,524,000) | (540,477,000) |
| Underwriting-related general and administrative expenses | (132,260,000) | (135,241,000) | (259,475,000) | (265,679,000) |
| Underwriting income | $ 142,927,000 | $ 189,201,000 | $ 330,289,000 | $ 352,656,000 |
| Current accident year loss ratio (as a percent) | 62.40% | 59.00% | 61.10% | 59.50% |
| Prior year reserve development ratio (as a percent) | (1.00%) | (1.50%) | (1.10%) | (1.40%) |
| Net losses and loss expenses ratio (as a percent) | 61.40% | 57.50% | 60.00% | 58.10% |
| Acquisition cost ratio (as a percent) | 20.80% | 19.80% | 20.70% | 19.80% |
| General and administrative expense ratio (as a percent) | 10.90% | 11.60% | 10.80% | 11.60% |
| Combined ratio (as a percent) | 93.10% | 88.90% | 91.50% | 89.50% |
| Goodwill and intangible assets | $ 227,756,000 | $ 237,340,000 | $ 227,756,000 | $ 237,340,000 |
| Operating Segments | Insurance | ||||
| Segment Information [Line Items] | ||||
| Gross premiums written | 2,228,147,000 | 1,932,435,000 | 4,211,888,000 | 3,588,337,000 |
| Net premiums written | 1,371,309,000 | 1,290,510,000 | 2,664,385,000 | 2,335,090,000 |
| Net premiums earned | 1,187,160,000 | 1,032,961,000 | 2,328,915,000 | 2,043,047,000 |
| Other insurance related income | 266,000 | 6,000 | 637,000 | 162,000 |
| Current accident year net losses and loss expenses | (718,734,000) | (576,986,000) | (1,374,780,000) | (1,153,052,000) |
| Net favorable prior year reserve development | 11,852,000 | 15,216,000 | 26,911,000 | 29,194,000 |
| Acquisition costs | (238,823,000) | (194,912,000) | (462,592,000) | (388,933,000) |
| Underwriting-related general and administrative expenses | (122,359,000) | (124,646,000) | (242,373,000) | (244,238,000) |
| Underwriting income | $ 119,362,000 | $ 151,639,000 | $ 276,718,000 | $ 286,180,000 |
| Current accident year loss ratio (as a percent) | 60.50% | 55.90% | 59.00% | 56.40% |
| Prior year reserve development ratio (as a percent) | (1.00%) | (1.50%) | (1.10%) | (1.40%) |
| Net losses and loss expenses ratio (as a percent) | 59.50% | 54.40% | 57.90% | 55.00% |
| Acquisition cost ratio (as a percent) | 20.10% | 18.90% | 19.90% | 19.00% |
| General and administrative expense ratio (as a percent) | 10.40% | 12.00% | 10.30% | 12.00% |
| Combined ratio (as a percent) | 90.00% | 85.30% | 88.10% | 86.00% |
| Goodwill and intangible assets | $ 227,756,000 | $ 237,340,000 | $ 227,756,000 | $ 237,340,000 |
| Operating Segments | Reinsurance | ||||
| Segment Information [Line Items] | ||||
| Gross premiums written | 439,484,000 | 583,536,000 | 1,553,709,000 | 1,722,285,000 |
| Net premiums written | 234,489,000 | 344,924,000 | 848,448,000 | 1,050,383,000 |
| Net premiums earned | 331,824,000 | 360,470,000 | 670,536,000 | 691,204,000 |
| Other insurance related income | 5,334,000 | 8,656,000 | 10,612,000 | 12,078,000 |
| Current accident year net losses and loss expenses | (229,232,000) | (244,997,000) | (458,531,000) | (472,793,000) |
| Net favorable prior year reserve development | 2,984,000 | 5,013,000 | 5,988,000 | 8,972,000 |
| Acquisition costs | (77,445,000) | (80,985,000) | (157,932,000) | (151,544,000) |
| Underwriting-related general and administrative expenses | (9,901,000) | (10,595,000) | (17,102,000) | (21,441,000) |
| Underwriting income | $ 23,564,000 | $ 37,562,000 | $ 53,571,000 | $ 66,476,000 |
| Current accident year loss ratio (as a percent) | 69.10% | 68.00% | 68.40% | 68.40% |
| Prior year reserve development ratio (as a percent) | (0.90%) | (1.40%) | (0.90%) | (1.30%) |
| Net losses and loss expenses ratio (as a percent) | 68.20% | 66.60% | 67.50% | 67.10% |
| Acquisition cost ratio (as a percent) | 23.30% | 22.50% | 23.60% | 21.90% |
| General and administrative expense ratio (as a percent) | 3.00% | 2.90% | 2.50% | 3.10% |
| Combined ratio (as a percent) | 94.50% | 92.00% | 93.60% | 92.10% |
| Goodwill and intangible assets | $ 0 | $ 0 | $ 0 | $ 0 |
| Segment Reconciling Items | ||||
| Segment Information [Line Items] | ||||
| Net investment income | 181,594,000 | 187,297,000 | 366,333,000 | 395,009,000 |
| Net investment gains | 46,735,000 | 43,468,000 | 19,514,000 | 13,462,000 |
| Foreign exchange (losses) gains | 2,344,000 | (94,885,000) | 38,539,000 | (151,920,000) |
| Interest expense and financing costs | (16,838,000) | (16,586,000) | (33,265,000) | (33,158,000) |
| Reorganization expenses | (5,546,000) | 0 | (28,715,000) | 0 |
| Amortization of intangible assets | (2,396,000) | (2,396,000) | (4,792,000) | (5,125,000) |
| Corporate expenses | ||||
| Segment Information [Line Items] | ||||
| Underwriting-related general and administrative expenses | $ (32,629,000) | $ (25,837,000) | $ (63,571,000) | $ (54,562,000) |
| X | ||||||||||
- Definition Current Accident Year, Loss Ratio No definition available.
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- Definition The net gain or loss (both realized and unrealized) related to investments in certain entities that calculate net asset value per share and the amount after accretion (amortization) of discount (premium) of interest income and dividend income on nonoperating securities, net of investment expense. No definition available.
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- Definition This item represents the net realized gains and losses on available for sale debt securities, the net realized and unrealized gains and losses on equity securities with FV recorded in net income, together with the change in fair value of investment derivatives, and expected and realized credit losses. No definition available.
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- Definition Prior Year Reserve Development Ratio No definition available.
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- Definition Net premiums earned less: net losses and loss expenses, acquisition costs and general and administrative expenses directly related to underwriting activities. No definition available.
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- Definition Ratio of non-life acquisition costs to non-life net premiums earned. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of amortization expense for finite-lived intangible asset. Excludes goodwill and capitalized cost for software to be sold, leased, or marketed. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Ratio of non-life losses and loss expenses, non-life acquisition expenses and non-life general and administrative expenses, to non-life net premiums earned. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of amortization expense (reversal of expense) for deferred policy acquisition costs. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount, before tax, of realized and unrealized gain (loss) from foreign currency transaction. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Ratio of non-life general and administrative expenses to non-life net premiums earned. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of income (loss) for proportionate share of equity method investee's income (loss). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after accumulated amortization, of finite- and indefinite-lived intangible assets, goodwill, and capitalized cost for software to be sold, leased, or marketed. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of interest expense classified as operating and nonoperating. Includes, but is not limited to, cost of borrowing accounted for as interest expense. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Ratio of non-life losses and loss expenses to non-life net premiums earned. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition The net amount of other operating income and expenses, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operations. No definition available.
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- Definition The amount of preferred stock dividends that is an adjustment to net income apportioned to common stockholders. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of direct and assumed premiums written. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums written. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of restructuring charges, remediation cost, and asset impairment loss. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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