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v3.20.1

Basis of Preparation and Significant Accounting Policies - Additional Information (Details) $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Jan. 01, 2020 USD ($) | Dec. 31, 2019 USD ($) period | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jan. 01, 2019 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 |  |  |
Right-of-use operating lease assets |  |  | $ 93.5 | $ 0.0 |  | $ 88.1
Operating lease liabilities |  |  | $ 113.2 |  |  | $ 95.5
Operating lease, weighted average discount rate (percent) |  |  | 5.00% |  |  |
Operating lease charge |  |  | $ 18.0 | 0.0 | $ 0.0 |
Amortization of right-of-use operating lease assets |  |  | 13.4 | $ 0.0 | 0.0 |
Interest on operating lease liability |  |  | $ 4.6 |  |  |
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% |  |  |
Restatement Adjustment | Retained earnings |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Retained earnings restatement | [1] |  |  |  | $ 15.6 |
Subsequent Event | Accounting Standards Update 2016-13 [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Available-for-sale investment portfolio |  | $ 0.5 |  |  |  |
Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease) |  | (3.7) |  |  |  |
Subsequent Event | Accounting Standards Update 2016-13 [Member] | Retained earnings |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Cumulative effect of new accounting principle in period of adoption |  | $ 4.2 |  |  |  |
[1] | Reinsurance premiums payables and retained earnings have been restated by $15.6 million from January 1, 2017 to account for additional ceded premiums on excess of loss ceded reinsurance contracts for periods December 31, 2016 and prior.

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