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Reserve for Loss and Loss Expense (Historical Claims Duration) (Details) $ in Thousands | Dec. 31, 2020 USD ($)
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Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Net outstanding liabilities | $ 12,185,164
Standard Commercial Lines [Member] | General Liability [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 6.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 12.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 15.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 17.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 14.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 9.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 6.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 5.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 2.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 1.80%
Standard Commercial Lines [Member] | Workers Compensation [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 21.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 25.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 13.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 8.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 4.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 3.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 3.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 2.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 1.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 1.20%
Standard Commercial Lines [Member] | Commercial Automobile [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 37.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 17.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 14.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 12.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 10.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 4.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 1.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 0.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 0.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 0.30%
Standard Commercial Lines [Member] | Business Owners' Policies [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 48.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 19.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 8.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 8.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 6.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 3.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 1.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 0.20%
Standard Commercial Lines [Member] | Commercial Property [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 70.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 25.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 2.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 1.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 0.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 0.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 0.10%
Standard Personal Lines | Personal Automobile [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 58.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 18.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 9.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 6.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 4.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 1.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 0.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 0.10%
Standard Personal Lines | Homeowners [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 71.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 20.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 3.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 1.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 1.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 0.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 0.30%
E&S Lines [Member] | General Liability [Member] |
Short-duration Insurance Contracts, Historical Claims Duration [Line Items] |
Short-duration Insurance Contracts, Historical Claims Duration, Year One | 4.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two | 12.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three | 17.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four | 21.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five | 13.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six | 9.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven | 7.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight | 3.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine | 2.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten | 2.00%

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