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Reserves for Losses and Adjustment Expenses - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Insurance [Abstract] |  |  |
Provision for losses and LAE for claims incurred | $ (0.9) | $ 59.5 | $ (111.1)
Prior years | (0.9) | 59.5 | (111.1)
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Line Items] |  |  |
Prior years | (0.9) | 59.5 | $ (111.1)
Reinsurance |  |  |
Insurance [Abstract] |  |  |
Provision for losses and LAE for claims incurred | 36.1 | 54.9 |
Prior years | 36.1 | 54.9 |
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Line Items] |  |  |
Prior years | 36.1 | 54.9 |
Insurance |  |  |
Insurance [Abstract] |  |  |
Provision for losses and LAE for claims incurred | (35.2) | (114.4) |
Prior years | (35.2) | (114.4) |
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Line Items] |  |  |
Prior years | (35.2) | $ (114.4) |
Crop Re |  |  |
Insurance [Abstract] |  |  |
Provision for losses and LAE for claims incurred | 0.9 |  |
Prior years | 0.9 |  |
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Line Items] |  |  |
Prior years | $ 0.9 |  |

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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