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v3.21.1

Basis of Preparation and Significant Accounting Policies - Additional Information (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) period | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items] |  |  |  |
Threshold Period of Value Decline in Equity Securities to be considered Other than Temporary Impairment | 12 months |  |  |
Non-Payment Of Dividends, Number Of Periods | period | 6 |  |  |
Amortization of right-of-use operating lease assets | $ 11.8 |  | $ 13.4 | $ 0.0
Available-for-sale investment, allowance for credit loss, increase (decrease) | (0.4) |  |  |
Reinsurance Recoverable, Allowance for Credit Loss, Period Increase (Decrease) | 0.1 |  |  |
Unpaid losses (1) (net of allowance for expected credit losses of $3.8 — $Nil) | $ 3.8 |  | 3.7 |
Computer Equipment | Minimum |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 3 years |  |  |
Computer Equipment | Maximum |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 5 years |  |  |
Furniture and Fixtures |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 4 years |  |  |
Leasehold Improvements |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 15 years |  |  |
Fixed maturities |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Percentage of Value Decline in Securities to be considered Other than Temporary Impairment | 20.00% |  |  |
Accounting Standards Update 2016-13 |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Available-for-sale investment, allowance for credit loss, increase (decrease) |  |  | 0.6 |
Accounting Standards Update 2016-13 | Retained earnings |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Cumulative Effect on Retained Earnings, before Tax | $ (4.3) | [1] | $ 0.0 | $ 0.0
[1] | The $4.3 million relates to the cumulative effect-adjustment to opening retained earnings as a result of the recognition of current expected credit losses (‘CECL’) in the Company’s available-for-sale investment portfolio and reinsurance recoverables following the adoption of ASU 2016-13.

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