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Reserves for Unpaid Losses and Loss Adjustment Expenses (Incurred Loss and Allocated LAE, Net of Reinsurance - Specialty Industries - Other) (Details) - Other - Specialty Industries $ in Millions | Dec. 31, 2016 USD ($) reported_claim | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($) | Dec. 31, 2011 USD ($) | Dec. 31, 2010 USD ($) | Dec. 31, 2009 USD ($) | Dec. 31, 2008 USD ($) | Dec. 31, 2007 USD ($)
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 294.8 |  |  |  |  |  |  |  |  |
2007 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 291 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 4.4 | $ 4.4 | $ 4.4 | $ 4.4 | $ 4.4 | $ 4.4 | $ 4.4 | $ 4.5 | $ 4.6 | $ 4.3
Total IBNR plus expected development on reported claims | $ 0.0 |  |  |  |  |  |  |  |  |
2008 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 975 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 12.3 | 12.1 | 12.1 | 11.8 | 11.9 | 11.9 | 12.2 | 10.8 | $ 10.4 |
Total IBNR plus expected development on reported claims | $ 0.0 |  |  |  |  |  |  |  |  |
2009 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 1,763 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 21.7 | 21.5 | 21.4 | 20.9 | 19.3 | 19.0 | 19.2 | $ 19.1 |  |
Total IBNR plus expected development on reported claims | $ 0.2 |  |  |  |  |  |  |  |  |
2010 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 2,449 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 28.4 | 28.4 | 28.2 | 27.9 | 27.1 | 26.6 | $ 25.6 |  |  |
Total IBNR plus expected development on reported claims | $ 0.0 |  |  |  |  |  |  |  |  |
2011 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 3,638 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 38.2 | 38.2 | 38.5 | 37.7 | 36.0 | $ 35.1 |  |  |  |
Total IBNR plus expected development on reported claims | $ 0.2 |  |  |  |  |  |  |  |  |
2012 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 3,861 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 41.6 | 41.1 | 40.1 | 39.6 | $ 42.0 |  |  |  |  |
Total IBNR plus expected development on reported claims | $ 0.3 |  |  |  |  |  |  |  |  |
2013 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 4,245 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 42.5 | 42.2 | 41.2 | $ 41.1 |  |  |  |  |  |
Total IBNR plus expected development on reported claims | $ 0.7 |  |  |  |  |  |  |  |  |
2014 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 3,497 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 40.6 | 40.4 | $ 42.6 |  |  |  |  |  |  |
Total IBNR plus expected development on reported claims | $ 1.9 |  |  |  |  |  |  |  |  |
2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 3,301 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 31.9 | $ 46.6 |  |  |  |  |  |  |  |
Total IBNR plus expected development on reported claims | $ 4.9 |  |  |  |  |  |  |  |  |
2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | reported_claim | 2,222 |  |  |  |  |  |  |  |  |
Incurred Loss and Allocated LAE, Net of Reinsurance | $ 33.2 |  |  |  |  |  |  |  |  |
Total IBNR plus expected development on reported claims | $ 19.4 |  |  |  |  |  |  |  |  |

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