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Reserves for Losses and Adjustment Expenses Short-duration Insurance Contracts, Claims by Accident Year (Details) | Dec. 31, 2021 USD ($) Integer | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($)
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | $ 4,484,000,000 | $ 4,266,000,000 |  |  |  |  |  |  |  |
Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,840,300,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,553,000,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 287,300,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 2,000,000.0 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 289,300,000 | 226,800,000 |  |  |  |  |  |  |  |
Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,537,500,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 848,900,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 688,600,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 37,000,000.0 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 725,600,000 | 618,700,000 |  |  |  |  |  |  |  |
Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 2,289,200,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,871,900,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 417,300,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 10,600,000 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 427,900,000 | 431,400,000 |  |  |  |  |  |  |  |
Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,921,500,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,119,300,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 802,200,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 6,500,000 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 808,700,000 | 738,500,000 |  |  |  |  |  |  |  |
Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 2,951,100,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 2,183,600,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 767,500,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 17,400,000 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 784,900,000 | 631,000,000.0 |  |  |  |  |  |  |  |
Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,907,200,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,038,200,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 869,000,000.0 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 106,300,000 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 975,300,000 | 1,084,200,000 |  |  |  |  |  |  |  |
Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 2,507,600,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 2,049,900,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 457,700,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 14,600,000 |  |  |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 472,300,000 | 535,400,000 |  |  |  |  |  |  |  |
Accident Year 2012 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 155,600,000 | 154,400,000 | $ 153,800,000 | $ 153,700,000 | $ 154,800,000 | $ 160,600,000 | $ 166,200,000 | $ 167,300,000 | $ 168,600,000 | $ 170,600,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 6,083 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 155,600,000 | 154,300,000 | 154,300,000 | 154,300,000 | 155,100,000 | 157,600,000 | 153,400,000 | 139,200,000 | 129,600,000 | 41,500,000
Accident Year 2012 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 69,300,000 | 71,500,000 | 71,100,000 | 69,200,000 | 67,200,000 | 69,600,000 | 61,700,000 | 70,600,000 | 63,400,000 | 78,600,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 3,400,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 3,130 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 65,000,000.0 | 59,900,000 | 55,200,000 | 50,600,000 | 49,700,000 | 41,300,000 | 30,000,000.0 | 14,300,000 | 6,700,000 | 1,300,000
Accident Year 2012 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 308,800,000 | 306,100,000 | 311,200,000 | 316,500,000 | 328,200,000 | 332,100,000 | 346,400,000 | 325,800,000 | 306,200,000 | 268,800,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (6,100,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 3,823 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 284,800,000 | 276,900,000 | 274,700,000 | 273,800,000 | 250,900,000 | 240,000,000.0 | 211,200,000 | 174,900,000 | 132,400,000 | 51,500,000
Accident Year 2012 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 104,500,000 | 103,400,000 | 96,500,000 | 101,700,000 | 89,600,000 | 94,000,000.0 | 97,000,000.0 | 93,600,000 | 89,900,000 | 88,500,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (4,400,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 579 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 92,800,000 | 91,300,000 | 85,300,000 | 80,300,000 | 70,600,000 | 65,400,000 | 59,400,000 | 50,800,000 | 39,600,000 | 22,800,000
Accident Year 2012 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 248,600,000 | 264,900,000 | 261,600,000 | 271,700,000 | 279,200,000 | 282,200,000 | 278,800,000 | 286,200,000 | 303,100,000 | 280,200,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (3,100,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 679 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 248,600,000 | 247,900,000 | 242,200,000 | 232,100,000 | 227,600,000 | 216,400,000 | 208,900,000 | 188,800,000 | 135,700,000 | 35,600,000
Accident Year 2012 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 196,200,000 | 240,000,000.0 | 245,100,000 | 242,600,000 | 233,700,000 | 232,800,000 | 236,000,000.0 | 244,600,000 | 233,300,000 | 235,100,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (27,100,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,813 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 165,400,000 | 162,200,000 | 144,400,000 | 134,700,000 | 117,800,000 | 96,600,000 | 65,500,000 | 42,100,000 | 17,800,000 | 2,200,000
Accident Year 2012 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 156,300,000 | 165,600,000 | 166,600,000 | 169,100,000 | 172,400,000 | 171,700,000 | 173,300,000 | 188,800,000 | 199,500,000 | 176,200,000
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (3,900,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 641 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 156,100,000 | 153,400,000 | 152,900,000 | 150,100,000 | 148,800,000 | 143,500,000 | 138,200,000 | 128,100,000 | 93,000,000.0 | $ 24,600,000
Accident Year 2013 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 110,700,000 | 112,800,000 | 112,600,000 | 112,300,000 | 114,300,000 | 113,300,000 | 117,500,000 | 117,900,000 | 130,800,000 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 300,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 5,764 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 110,000,000.0 | 111,200,000 | 110,900,000 | 109,100,000 | 106,400,000 | 101,700,000 | 89,700,000 | 76,400,000 | 39,200,000 |
Accident Year 2013 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 100,900,000 | 104,300,000 | 105,700,000 | 105,400,000 | 104,300,000 | 121,300,000 | 115,800,000 | 117,400,000 | 134,000,000.0 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 7,200,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 3,367 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 88,000,000.0 | 87,800,000 | 85,800,000 | 81,500,000 | 69,000,000.0 | 53,400,000 | 39,800,000 | 26,000,000.0 | 2,300,000 |
Accident Year 2013 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 343,300,000 | 340,200,000 | 345,200,000 | 346,600,000 | 333,000,000.0 | 325,900,000 | 342,500,000 | 333,800,000 | 321,000,000.0 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 2,800,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,178 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 311,000,000.0 | 310,800,000 | 300,600,000 | 284,500,000 | 264,800,000 | 235,400,000 | 205,000,000.0 | 131,700,000 | 41,500,000 |
Accident Year 2013 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 102,800,000 | 97,600,000 | 90,900,000 | 91,900,000 | 100,800,000 | 101,700,000 | 105,000,000.0 | 100,600,000 | 106,100,000 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 2,200,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 586 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 81,800,000 | 78,300,000 | 75,000,000.0 | 72,800,000 | 64,100,000 | 65,600,000 | 31,300,000 | 21,200,000 | 8,100,000 |
Accident Year 2013 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 164,700,000 | 168,200,000 | 171,000,000.0 | 173,800,000 | 177,100,000 | 178,500,000 | 189,700,000 | 199,900,000 | 217,400,000 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 600,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 832 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 161,200,000 | 161,200,000 | 166,800,000 | 165,200,000 | 163,700,000 | 159,000,000.0 | 146,900,000 | 98,800,000 | 34,500,000 |
Accident Year 2013 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 165,800,000 | 201,600,000 | 204,400,000 | 201,700,000 | 206,600,000 | 223,600,000 | 226,300,000 | 230,800,000 | 215,600,000 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (6,800,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,691 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 146,300,000 | 139,900,000 | 127,800,000 | 115,000,000.0 | 93,100,000 | 65,100,000 | 42,800,000 | 15,900,000 | 3,400,000 |
Accident Year 2013 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 104,800,000 | 111,000,000.0 | 114,400,000 | 114,800,000 | 118,600,000 | 119,400,000 | 131,300,000 | 139,600,000 | 144,400,000 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (500,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 577 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 100,700,000 | 101,700,000 | 101,900,000 | 101,000,000.0 | 101,000,000.0 | 94,000,000.0 | 86,900,000 | 70,900,000 | $ 25,000,000.0 |
Accident Year 2014 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 133,400,000 | 132,400,000 | 133,000,000.0 | 134,600,000 | 135,300,000 | 134,700,000 | 157,900,000 | 166,100,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 9,973 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 132,300,000 | 131,000,000.0 | 129,800,000 | 128,300,000 | 124,200,000 | 114,500,000 | 86,900,000 | 40,500,000 |  |
Accident Year 2014 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 130,400,000 | 138,800,000 | 141,800,000 | 137,700,000 | 130,500,000 | 140,300,000 | 128,400,000 | 146,200,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 5,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 3,865 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 110,100,000 | 111,400,000 | 98,400,000 | 74,000,000.0 | 60,400,000 | 33,100,000 | 13,500,000 | 2,700,000 |  |
Accident Year 2014 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 312,500,000 | 302,200,000 | 313,000,000.0 | 306,000,000.0 | 310,500,000 | 298,900,000 | 314,000,000.0 | 309,800,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (5,900,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,043 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 275,600,000 | 263,100,000 | 250,900,000 | 232,700,000 | 210,000,000.0 | 189,300,000 | 116,900,000 | 53,600,000 |  |
Accident Year 2014 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 123,700,000 | 121,700,000 | 120,900,000 | 131,900,000 | 120,600,000 | 130,200,000 | 131,600,000 | 135,700,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (2,700,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 800 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 104,200,000 | 92,600,000 | 85,900,000 | 80,000,000.0 | 72,500,000 | 53,800,000 | 30,900,000 | 3,000,000.0 |  |
Accident Year 2014 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 143,900,000 | 144,900,000 | 144,900,000 | 149,800,000 | 149,500,000 | 160,900,000 | 176,800,000 | 189,900,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 800,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 900 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 141,500,000 | 141,300,000 | 139,600,000 | 140,900,000 | 137,000,000.0 | 127,100,000 | 100,700,000 | 37,400,000 |  |
Accident Year 2014 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 160,500,000 | 202,900,000 | 207,100,000 | 204,500,000 | 211,100,000 | 217,600,000 | 209,000,000.0 | 206,200,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (14,800,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,805 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 135,700,000 | 125,700,000 | 107,700,000 | 86,700,000 | 60,300,000 | 37,800,000 | 13,800,000 | 2,500,000 |  |
Accident Year 2014 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 114,900,000 | 120,100,000 | 124,300,000 | 125,800,000 | 122,900,000 | 132,100,000 | 140,100,000 | 152,400,000 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 600,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 619 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 106,200,000 | 104,200,000 | 102,600,000 | 99,700,000 | 89,300,000 | 81,300,000 | 56,500,000 | $ 16,600,000 |  |
Accident Year 2015 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 202,200,000 | 201,500,000 | 204,600,000 | 204,200,000 | 201,800,000 | 207,400,000 | 241,800,000 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 2,000,000.0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 11,598 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 197,800,000 | 196,400,000 | 198,000,000.0 | 181,300,000 | 172,100,000 | 144,100,000 | 57,500,000 |  |  |
Accident Year 2015 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 227,700,000 | 236,700,000 | 238,400,000 | 205,500,000 | 187,600,000 | 225,100,000 | 205,100,000 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 13,500,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,736 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 181,400,000 | 169,200,000 | 139,700,000 | 93,500,000 | 57,000,000.0 | 17,200,000 | 3,200,000 |  |  |
Accident Year 2015 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 321,400,000 | 313,000,000.0 | 310,400,000 | 286,800,000 | 282,600,000 | 300,200,000 | 297,100,000 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (4,600,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,074 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 280,600,000 | 257,900,000 | 222,500,000 | 194,500,000 | 174,600,000 | 123,400,000 | 44,900,000 |  |  |
Accident Year 2015 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 185,900,000 | 186,700,000 | 191,900,000 | 190,600,000 | 186,400,000 | 176,300,000 | 175,000,000.0 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (400,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,080 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 146,200,000 | 139,600,000 | 110,400,000 | 89,700,000 | 70,300,000 | 43,600,000 | 13,800,000 |  |  |
Accident Year 2015 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 179,800,000 | 171,900,000 | 171,800,000 | 156,600,000 | 177,200,000 | 187,300,000 | 214,600,000 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 11,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,051 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 162,200,000 | 158,600,000 | 156,200,000 | 139,200,000 | 127,100,000 | 95,000,000.0 | 35,800,000 |  |  |
Accident Year 2015 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 160,600,000 | 208,000,000.0 | 212,000,000.0 | 214,200,000 | 211,700,000 | 202,200,000 | 195,400,000 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (13,600,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,964 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 123,300,000 | 109,000,000.0 | 89,700,000 | 65,700,000 | 38,500,000 | 18,000,000.0 | 3,500,000 |  |  |
Accident Year 2015 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 149,000,000.0 | 152,800,000 | 157,300,000 | 159,000,000.0 | 164,500,000 | 170,000,000.0 | 165,900,000 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 4,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 777 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 134,000,000.0 | 134,000,000.0 | 130,900,000 | 122,000,000.0 | 104,100,000 | 56,400,000 | $ 17,700,000 |  |  |
Accident Year 2016 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 249,200,000 | 248,400,000 | 246,900,000 | 245,500,000 | 250,700,000 | 239,900,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 1,600,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 10,785 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 239,000,000.0 | 233,800,000 | 224,800,000 | 202,500,000 | 169,700,000 | 67,300,000 |  |  |  |
Accident Year 2016 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 233,800,000 | 203,100,000 | 192,000,000.0 | 185,300,000 | 190,000,000.0 | 218,900,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 54,100,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,753 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 134,800,000 | 111,000,000.0 | 83,500,000 | 40,700,000 | 23,100,000 | 4,200,000 |  |  |  |
Accident Year 2016 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 221,700,000 | 219,400,000 | 229,600,000 | 229,400,000 | 230,800,000 | 260,800,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 200,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,429 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 199,000,000.0 | 191,200,000 | 164,300,000 | 142,800,000 | 82,700,000 | 30,900,000 |  |  |  |
Accident Year 2016 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 185,700,000 | 186,300,000 | 203,100,000 | 217,400,000 | 212,600,000 | 191,900,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 13,500,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,255 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 136,000,000.0 | 126,600,000 | 130,600,000 | 102,500,000 | 71,400,000 | 15,200,000 |  |  |  |
Accident Year 2016 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 230,400,000 | 244,900,000 | 249,200,000 | 271,000,000.0 | 272,700,000 | 272,600,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (15,200,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,308 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 236,700,000 | 230,400,000 | 217,100,000 | 206,000,000.0 | 164,700,000 | 57,200,000 |  |  |  |
Accident Year 2016 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 213,500,000 | 264,700,000 | 257,200,000 | 247,000,000.0 | 247,300,000 | 234,700,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (2,100,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 2,056 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 148,000,000.0 | 127,000,000.0 | 96,700,000 | 64,500,000 | 33,700,000 | 9,300,000 |  |  |  |
Accident Year 2016 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 214,700,000 | 225,000,000.0 | 230,000,000.0 | 237,700,000 | 239,900,000 | 238,800,000 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (5,400,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 937 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 203,800,000 | 193,800,000 | 183,600,000 | 165,500,000 | 150,900,000 | $ 58,700,000 |  |  |  |
Accident Year 2017 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 254,100,000 | 254,900,000 | 253,500,000 | 260,300,000 | 297,500,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 10,300,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 9,693 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 248,400,000 | 244,100,000 | 223,200,000 | 189,900,000 | 97,000,000.0 |  |  |  |  |
Accident Year 2017 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 201,600,000 | 199,300,000 | 180,400,000 | 176,300,000 | 182,900,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 18,900,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 5,416 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 116,800,000 | 98,400,000 | 53,400,000 | 23,200,000 | 3,600,000 |  |  |  |  |
Accident Year 2017 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 209,800,000 | 214,900,000 | 207,400,000 | 201,100,000 | 210,700,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 37,900,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 6,041 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 156,900,000 | 168,800,000 | 140,600,000 | 97,800,000 | 40,300,000 |  |  |  |  |
Accident Year 2017 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 188,600,000 | 189,400,000 | 188,900,000 | 184,100,000 | 207,700,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 12,800,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,739 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 137,200,000 | 117,500,000 | 83,600,000 | 51,400,000 | 27,200,000 |  |  |  |  |
Accident Year 2017 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 481,200,000 | 505,000,000.0 | 516,200,000 | 534,500,000 | 557,700,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (3,800,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,956 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 437,600,000 | 440,800,000 | 416,600,000 | 357,400,000 | 123,200,000 |  |  |  |  |
Accident Year 2017 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 194,200,000 | 254,100,000 | 254,900,000 | 244,000,000.0 | 246,600,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 3,400,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 2,005 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 117,300,000 | 97,900,000 | 59,200,000 | 30,700,000 | 8,900,000 |  |  |  |  |
Accident Year 2017 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 343,200,000 | 364,400,000 | 376,000,000.0 | 392,400,000 | 379,700,000 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (6,100,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,328 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 317,100,000 | 306,300,000 | 271,000,000.0 | 238,800,000 | $ 94,600,000 |  |  |  |  |
Accident Year 2018 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 190,400,000 | 191,900,000 | 208,200,000 | 205,500,000 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 400,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 8,171 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 181,800,000 | 185,000,000.0 | 162,900,000 | 62,600,000 |  |  |  |  |  |
Accident Year 2018 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 135,500,000 | 137,900,000 | 126,800,000 | 124,000,000.0 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 22,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 5,419 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 69,700,000 | 44,100,000 | 28,200,000 | 3,200,000 |  |  |  |  |  |
Accident Year 2018 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 219,900,000 | 209,400,000 | 208,500,000 | 171,400,000 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ (2,400,000) |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 5,178 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 155,700,000 | 133,400,000 | 105,100,000 | 26,900,000 |  |  |  |  |  |
Accident Year 2018 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 152,700,000 | 156,900,000 | 174,600,000 | 158,500,000 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 6,000,000.0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,617 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 117,100,000 | 101,600,000 | 75,700,000 | 21,000,000.0 |  |  |  |  |  |
Accident Year 2018 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 403,500,000 | 389,500,000 | 394,200,000 | 343,100,000 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 22,200,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,808 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 345,400,000 | 325,700,000 | 311,600,000 | 122,800,000 |  |  |  |  |  |
Accident Year 2018 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 190,600,000 | 267,000,000.0 | 259,800,000 | 230,100,000 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 24,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,766 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 104,900,000 | 73,700,000 | 33,700,000 | 7,200,000 |  |  |  |  |  |
Accident Year 2018 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 391,100,000 | 394,300,000 | 396,400,000 | 397,400,000 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 13,000,000.0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,399 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 331,100,000 | 314,600,000 | 280,800,000 | $ 27,200,000 |  |  |  |  |  |
Accident Year 2019 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 122,600,000 | 132,100,000 | 128,500,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 6,812 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 103,400,000 | 92,600,000 | 49,600,000 |  |  |  |  |  |  |
Accident Year 2019 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 127,900,000 | 148,800,000 | 126,500,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 4,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 5,104 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 70,400,000 | 18,600,000 | 6,400,000 |  |  |  |  |  |  |
Accident Year 2019 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 146,000,000.0 | 154,100,000 | 146,500,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 3,000,000.0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 3,575 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 118,100,000 | 72,800,000 | 33,600,000 |  |  |  |  |  |  |
Accident Year 2019 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 236,000,000.0 | 263,800,000 | 250,500,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 52,800,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 23,894 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 138,400,000 | 87,300,000 | 27,400,000 |  |  |  |  |  |  |
Accident Year 2019 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 270,600,000 | 272,300,000 | 262,800,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 3,600,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,395 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 205,600,000 | 153,000,000.0 | 28,200,000 |  |  |  |  |  |  |
Accident Year 2019 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 179,200,000 | 256,600,000 | 236,200,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 52,300,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,300 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 61,400,000 | 36,500,000 | 9,200,000 |  |  |  |  |  |  |
Accident Year 2019 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 495,400,000 | 498,900,000 | 476,100,000 |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 49,200,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,519 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 402,100,000 | 382,700,000 | $ 274,300,000 |  |  |  |  |  |  |
Accident Year 2020 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 211,200,000 | 206,700,000 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 36,200,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | 7,295 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 125,500,000 | 61,900,000 |  |  |  |  |  |  |  |
Accident Year 2020 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 133,900,000 | 134,900,000 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 94,300,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | 3,570 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 3,200,000 | 0 |  |  |  |  |  |  |  |
Accident Year 2020 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 111,800,000 | 111,000,000.0 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 12,000,000.0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 4,128 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 66,700,000 | 28,500,000 |  |  |  |  |  |  |  |
Accident Year 2020 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 352,000,000.0 | 351,000,000.0 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 181,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 105,317 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 121,900,000 | 48,000,000.0 |  |  |  |  |  |  |  |
Accident Year 2020 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 366,900,000 | 322,900,000 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 20,100,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,333 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 169,200,000 | 42,400,000 |  |  |  |  |  |  |  |
Accident Year 2020 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 237,600,000 | 256,400,000 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 177,800,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 753 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 28,000,000.0 | 9,200,000 |  |  |  |  |  |  |  |
Accident Year 2020 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 382,400,000 | 415,600,000 |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 66,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,400 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 270,400,000 | $ 213,100,000 |  |  |  |  |  |  |  |
Accident Year 2021 | Property Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 210,900,000 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 88,800,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | 4,978 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 59,200,000 |  |  |  |  |  |  |  |  |
Accident Year 2021 | Casualty Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 176,500,000 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 150,500,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | 2,707 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 9,500,000 |  |  |  |  |  |  |  |  |
Accident Year 2021 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 94,000,000.0 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 44,700,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 2,108 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 23,500,000 |  |  |  |  |  |  |  |  |
Accident Year 2021 | Financial and Professional Insurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 289,600,000 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 221,500,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 31,311 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 43,700,000 |  |  |  |  |  |  |  |  |
Accident Year 2021 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 461,500,000 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 198,600,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,005 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 75,600,000 |  |  |  |  |  |  |  |  |
Accident Year 2021 | Casualty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 209,000,000.0 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 177,000,000.0 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 355 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 7,900,000 |  |  |  |  |  |  |  |  |
Accident Year 2021 | Specialty Reinsurance |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 155,800,000 |  |  |  |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 106,100,000 |  |  |  |  |  |  |  |  |
Number of Reported Claims | Integer | 1,020 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 28,400,000 |  |  |  |  |  |  |  |  |

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