CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands |
Dec. 31, 2025 |
Dec. 31, 2024 |
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| Investments: | ||||||||||||||||
| Fixed income securities, available-for-sale | [1] | $ 5,013,400 | $ 4,692,200 | |||||||||||||
| Fixed income securities, trading | [1] | 1,040,200 | 1,199,900 | |||||||||||||
| Short-term investments, available for sale | 45,400 | 261,900 | ||||||||||||||
| Short-term investments, trading at fair value | 0 | 1,000 | ||||||||||||||
| Catastrophe bonds, trading at fair value (amortized cost — 2025: $0.0 and 2024: $1.0) | 0 | 1,000 | ||||||||||||||
| Privately-held Investments, available for sale, at fair value | [2] | 50,500 | 24,200 | |||||||||||||
| Privately-held Investments | [2] | 121,800 | 286,800 | |||||||||||||
| Equity investments, trading | 8,100 | 0 | ||||||||||||||
| Investments, equity method | 9,600 | 7,300 | ||||||||||||||
| Other Investments | [3] | 279,600 | 267,200 | |||||||||||||
| Investments, Excluding Derivative Assets | 6,568,600 | 6,741,500 | ||||||||||||||
| Reinsurance recoverables: | ||||||||||||||||
| Cash and Cash Equivalent | [4] | 1,658,800 | 914,200 | |||||||||||||
| Unpaid losses recoverable from reinsurers (net of allowance for expected credit losses of 2025: $16.2 and 2024: $27.5) | 4,281,900 | 4,172,000 | ||||||||||||||
| Ceded unearned premiums | 968,600 | 901,700 | ||||||||||||||
| Receivables: | ||||||||||||||||
| Premiums Receivable, Net | [5] | 1,700,800 | 1,617,000 | |||||||||||||
| Deferred acquisition costs | 357,200 | 322,100 | ||||||||||||||
| Derivative assets | 5,000 | 17,000 | ||||||||||||||
| Right-of-use operating lease assets | 43,400 | 53,500 | ||||||||||||||
| Income taxes refundable | 2,500 | 900 | ||||||||||||||
| Deferred tax assets | 342,500 | 397,900 | ||||||||||||||
| Other assets | 360,400 | 590,800 | ||||||||||||||
| Intangible assets and goodwill | 19,900 | 19,900 | ||||||||||||||
| Total assets | 16,309,600 | 15,748,500 | ||||||||||||||
| Insurance Reserve [Abstract] | ||||||||||||||||
| Liability for Claims and Claims Adjustment Expense | [5] | 8,725,000 | 8,122,600 | |||||||||||||
| Unearned Premiums | [5] | 2,725,800 | 2,645,800 | |||||||||||||
| Total insurance reserves | 11,450,800 | 10,768,400 | ||||||||||||||
| Reinsurance premiums | 520,300 | 901,100 | ||||||||||||||
| Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract] | ||||||||||||||||
| Income taxes payable | 18,700 | 6,800 | ||||||||||||||
| Deferred tax liabilities | 4,000 | 1,100 | ||||||||||||||
| Accrued expenses and other payables | [6] | 317,100 | 237,200 | |||||||||||||
| Payables for securities purchased | 0 | 36,900 | ||||||||||||||
| Operating lease liabilities | 64,700 | 75,600 | ||||||||||||||
| Derivative liabilities | 12,100 | 49,500 | ||||||||||||||
| Short-Term Debt | 296,800 | 300,000 | ||||||||||||||
| Total liabilities | 12,684,500 | 12,376,600 | ||||||||||||||
| Commitments and contingent liabilities | ||||||||||||||||
| Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] | ||||||||||||||||
| Ordinary shares, value | [7] | 92 | 91 | |||||||||||||
| Preference shares, value | 699,900 | 970,500 | ||||||||||||||
| Additional paid-in capital (7) | [7] | 803,400 | 761,700 | |||||||||||||
| Retained earnings | 2,320,000 | 2,029,700 | ||||||||||||||
| Accumulated other comprehensive (loss) | (198,300) | (390,100) | ||||||||||||||
| Total shareholders' equity | 3,625,100 | 3,371,900 | ||||||||||||||
| Total liabilities and shareholders’ equity | $ 16,309,600 | $ 15,748,500 | ||||||||||||||
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- Definition Catastrophe Bond No definition available.
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- Definition Equity investments, trading No definition available.
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- Definition Fixed Income Debt Securities, Available-for-Sale No definition available.
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- Definition Fixed Income Debt Securities, Trading No definition available.
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- Definition Insurance Reserve No definition available.
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- Definition Insurance reserves No definition available.
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- Definition Investments, Excluding Derivative Assets No definition available.
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- Definition Privately-held Investments, available for sale, at fair value No definition available.
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- Definition Privately-held Investments No definition available.
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- Definition Short-term investments, available for sale No definition available.
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- Definition Short-term investments, trading at fair value No definition available.
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- Definition Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all currently due domestic and foreign income tax obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount, after tax, of accumulated increase (decrease) in equity from transaction and other event and circumstance from nonowner source. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of excess of issue price over par or stated value of stock and from other transaction involving stock or stockholder. Includes, but is not limited to, additional paid-in capital (APIC) for common and preferred stock. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of asset recognized for present right to economic benefit. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cash and cash equivalent. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Represents the caption on the face of the balance sheet to indicate that the entity has entered into (1) purchase or supply arrangements that will require expending a portion of its resources to meet the terms thereof, and (2) is exposed to potential losses or, less frequently, gains, arising from (a) possible claims against a company's resources due to future performance under contract terms, and (b) possible losses or likely gains from uncertainties that will ultimately be resolved when one or more future events that are deemed likely to occur do occur or fail to occur. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition Aggregate par or stated value of issued nonredeemable common stock (or common stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable common shares, par value and other disclosure concepts are in another section within stockholders' equity. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, with jurisdictional netting. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences with jurisdictional netting. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of deferred policy acquisition cost capitalized on contract remaining in force. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Carrying amount as of the balance sheet date of income taxes previously overpaid to tax authorities (such as U.S. Federal, state and local tax authorities) representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes. Also called income tax refund receivable. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount, after impairment and amortization, of goodwill, indefinite-lived, and finite-lived intangible assets. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- References No definition available.
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- Definition Amount of liability recognized for present obligation requiring transfer or otherwise providing economic benefit to others. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of liabilities and equity items, including the portion of equity attributable to noncontrolling interests, if any. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- References No definition available.
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of lessee's right to use underlying asset under operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of assets classified as other. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of investments classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References No definition available.
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- Definition The carrying amount as of the balance sheet date due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, net of the allowance for doubtful accounts. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition The unexpired portion of premiums ceded on policies in force as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- References No definition available.
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- Definition The carrying amount as of the balance sheet date of the known and estimated amounts owed to insurers under reinsurance treaties or other arrangements. No definition available.
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- Definition Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of accumulated undistributed earnings (deficit). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of equity (deficit) attributable to parent and noncontrolling interest. Excludes temporary equity. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Carrying amount of premiums written on insurance contracts that have not been earned as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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