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Compensation for Covered Year [Member] Net cash provided by (used in) operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Prior years Net prior year development, unfavorable (favorable) Prior Year Claims and Claims Adjustment Expense Pledging Purpose [Domain] Pledging Purpose [Domain] Income Statement [Abstract] Shareholders’ equity Equity, Attributable to Parent [Abstract] Pledging Purpose [Axis] Pledging Purpose [Axis] Document Transition Report Document Transition Report Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Net realized and unrealized gains (losses) on investments Net realized and unrealized gains (losses) on investments Gain (Loss) on Investments Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Investment, Name [Axis] Investment, Name [Axis] Total fixed maturities Fixed Maturities [Member] Share class conversions (in shares) Stock 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ratio Combined Ratio Total expenses Benefits, Losses and Expenses Income tax expense (benefit) Income tax (expense) benefit Income Tax Expense (Benefit) Net foreign exchange gains (losses) Gain (Loss), Foreign Currency Transaction, before Tax Schedule of Investments in Two Sigma Funds Alternative Investments [Table Text Block] Alternative Investments Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Noncash Item [Abstract] Net income (loss) and other comprehensive income (loss) attributable to common shareholders Net income (loss) attributable to common shareholders Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Award Timing Method Award Timing Method [Text Block] Net increase (decrease) in cash and cash equivalents and restricted cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted 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