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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, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Insurance [Abstract] |  |  |
Provision for losses and LAE for claims incurred | $ 105.4 | $ 129.3 | $ 156.5
Additional loss reserves assumed |  | 5.7 |
Liability for unpaid claims and claims adjustment expense amount ceded | $ (125.5) | $ (85.8) | $ 0.0

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- Definition Liability For Unpaid Claims And Claims Adjustment Expense Amount Disposed of or Ceded + References No definition available. + Details
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- Definition Unpaid claims and claims adjustment expense specialty reinsurance contracts. + References No definition available. + Details
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- References No definition available. + Details
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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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915 + Details
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