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Income Taxes - Net Operating Losses and Income Tax Concessions (Details) - USD ($) $ in Millions |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Jan. 01, 2018 | Jan. 01, 2013 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income taxes |  |  |  |  |  |
Net operating losses |  |  | $ 275.3 | $ 240.3 |  |
Net operating loss carryforward |  |  | 33.7 | 23.0 |  |
Valuation allowance |  |  | 24.3 | 24.6 |  |
Period applicable for additional special income tax concession |  | 5 years |  |  |  |
Period applicable for additional special income tax concession, renewal term | 5 years |  |  |  |  |
Unrecognized Tax Benefits |  |  | 57.0 | 58.8 | $ 62.2 | $ 47.8
Gross increases – tax positions in prior period |  |  | 3.6 | 10.9 | 19.7 |
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions |  |  | 10.6 | 0.0 | 15.4 |
Gross increases – tax positions in current period |  |  | 11.5 | 10.7 | 12.9 |
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions |  |  | 0.0 | 0.0 | 0.0 |
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities |  |  | 1.5 | 23.0 | 0.0 |
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations |  |  | 4.8 | $ 2.1 | $ 2.8 |
December 31, 2020 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  |  |  |  |
December 31, 2021 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 0.3 |  |  |
December 31, 2022 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 0.7 |  |  |
December 31, 2023 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 0.7 |  |  |
December 31, 2024 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 0.4 |  |  |
December 31, 2025 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 0.4 |  |  |
December 31, 2026 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Unrecognized Tax Benefits |  |  | 0.4 |  |  |
December 31, 2027 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Gross increases – tax positions in prior period |  |  | 0.4 |  |  |
December 31, 2028 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions |  |  | 0.3 |  |  |
December 31, 2029 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Gross increases – tax positions in current period |  |  | 0.6 |  |  |
December 31, 2030 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Gross increases – tax positions in current period |  |  | 0.4 |  |  |
December 31, 2031 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions |  |  | 0.2 |  |  |
December 31, 2032 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities |  |  | 0.4 |  |  |
December 31, 2033 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations |  |  | 0.3 |  |  |
December 31, 2034 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Unrecognized Tax Benefits |  |  | 0.3 |  |  |
December 31, 2035 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 0.5 |  |  |
December 31, 2036 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 2.6 |  |  |
December 31, 2037 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 4.1 |  |  |
December 31, 2038 |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | 3.3 |  |  |
Indefinite |  |  |  |  |  |
Income taxes |  |  |  |  |  |
Net operating loss carryforward |  |  | $ 17.4 |  |  |

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