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Income Taxes - Income Tax Contingencies (Details) $ in Millions, ₩ in Billions | 3 Months Ended | 12 Months Ended
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Jun. 30, 2019 USD ($) | Jun. 30, 2017 USD ($) | Jun. 30, 2017 KRW (₩) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2017 KRW (₩)
Income Tax Disclosure [Abstract] |  |  |  |  |  |  |
Increase (decrease) in additional liabilities related to unrecognized tax liabilities |  |  |  | $ 9.5 | $ (1.8) |  |
Increase (decrease) in assets related to unrecognized tax assets |  |  |  | (4.1) | 4.3 |  |
Increase (decrease) in unrecognized tax liabilities related to a foreign currency translation expense |  |  |  | (0.2) | 0.9 |  |
Unrecognized tax liabilities |  |  |  | 84.0 | 70.2 |  |
Unrecognized tax assets |  |  |  | 25.5 | 29.7 |  |
Reconciliation of total amounts of unrecognized income tax benefits |  |  |  |  |  |  |
Gross Unrecognized Tax Liabilities – opening balance |  |  |  | 57.0 | 58.8 | $ 62.2 |
Gross increases – tax positions in prior period |  |  |  | 12.2 | 3.6 | 10.9 |
Gross decreases – tax positions in prior period |  |  |  | (13.5) | (10.6) | 0.0 |
Gross increases – tax positions in current period |  |  |  | 14.9 | 11.5 | 10.7 |
Gross decreases – tax positions in current period |  |  |  | 0.0 | 0.0 | 0.0 |
Settlements |  |  |  | (1.4) | (1.5) | (23.0) |
Lapse of statute of limitations |  |  |  | (2.7) | (4.8) | (2.1) |
Gross Unrecognized Tax Liabilities – ending balance |  |  |  | 66.5 | 57.0 | 58.8 |
Expected reduction in income tax expense if uncertain tax positions are settled by the taxing authorities in the entity's favor |  |  |  | $ 41.1 |  |  |
Expected reduction in effective income tax rate if uncertain tax positions are settled by the taxing authorities in the entity's favor (as a percent) |  |  |  | 17.30% |  |  |
Amount of unrecognized income tax liabilities may decrease within the next twelve months |  |  |  | $ 9.0 |  |  |
Interest related to unrecognized tax benefits, recorded as income (expense) |  |  |  | 4.6 | 1.2 | 3.4 |
Penalties related to unrecognized tax benefits, recorded as income tax income (expense) |  |  |  | (0.2) | 1.9 | 0.1 |
Accrued interest related to unrecognized tax benefits |  |  |  | 13.1 | 8.5 |  |
Accrued penalties related to unrecognized tax benefits |  |  |  | $ 4.4 | $ 4.6 |  |
Assessment | South Korea (SRTO) |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Pre-assessment notice, amount |  | $ 17.4 | ₩ 20.1 |  |  | $ 9.8 | ₩ 11.3
Foreign Tax Authority | Danish Tax Authority |  |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |  |
Proposed income adjustment | $ 1.7 |  |  |  |  |  |

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