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Commitments and Contingencies (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jun. 28, 2019
Loss Contingencies [Line Items] |  |  |  |
Rent expense | $ 7.2 | $ 5.5 | $ 3.5 |
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] |  |  |  |
Capital lease payments due next year | 7.1 |  |  |
Capital lease payments due in two years | 6.1 |  |  |
Capital lease payments due in three years | 5.7 |  |  |
Capital Lease payments due in four years and thereafter | 18.4 |  |  |
Commitments to fund other-long term investments | 183.4 |  |  |
Sirius Group | Sirius Group | Swedish Tax Authority |  |  |  |
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] |  |  |  |
Loss contingency accrual | 16.5 | 17.3 |  |
Loss contingency accrual, period increase (decrease) | (0.8) | $ 17.3 |  |
American International Group | NSM Insurance HoldCo, LLC |  |  |  |
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] |  |  |  |
Purchase obligation | $ 82.5 |  |  |
Intangible assets acquired |  |  |  | $ 82.5

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