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Income Taxes - Income Tax Contingencies (Details) $ in Millions, ₩ in Billions | 3 Months Ended | 12 Months Ended
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Dec. 31, 2016 USD ($) | Dec. 31, 2016 KRW (₩) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Income Tax Disclosure [Abstract] |  |  |  |  |
Increase (decrease) in additional liabilities related to unrecognized tax liabilities |  |  | $ (3.4) | $ 14.4 |
Increase (decrease) in assets related to unrecognized tax assets |  |  | 19.8 | 3.2 |
Increase (decrease) in unrecognized tax liabilities related to a foreign currency translation expense |  |  | 1.4 | (0.1) |
Unrecognized tax liabilities | $ 62.2 |  | 72.6 | 62.2 |
Unrecognized tax assets | 5.6 |  | 25.4 | 5.6 |
Reconciliation of total amounts of unrecognized income tax benefits |  |  |  |  |
Gross Unrecognized Tax Liabilities – opening balance |  |  | 62.2 | 47.8 | $ 24.3
Gross increases – tax positions in prior period |  |  | 10.9 | 19.7 | 9.2
Gross decreases – tax positions in prior period |  |  | 0.0 | (15.4) | (4.8)
Gross increases – tax positions in current period |  |  | 10.7 | 12.9 | 22.0
Gross decreases – tax positions in current period |  |  | 0.0 | 0.0 | 0.0
Settlements |  |  | (23.0) | 0.0 | 0.0
Lapse of statute of limitations |  |  | (2.1) | (2.8) | (2.9)
Gross Unrecognized Tax Liabilities – ending balance | 62.2 |  | 58.8 | 62.2 | 47.8
Expected reduction in income tax expense if uncertain tax positions are settled by the taxing authorities in the entity's favor |  |  | $ 33.4 |  |
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) |  |  | 158.20% |  |
Interest and penalties expense |  |  |  |  |
Interest related to unrecognized tax benefits, recorded as income (expense) |  |  | $ (3.4) | 0.7 | (0.9)
Penalties related to unrecognized tax benefits, recorded as income tax income (expense) |  |  | (0.1) | (2.3) | $ 0.3
Accrued interest and penalties |  |  |  |  |
Accrued interest related to unrecognized tax benefits | 4.3 |  | 7.3 | 4.3 |
Accrued penalties related to unrecognized tax benefits | 6.5 |  | $ 6.5 | $ 6.5 |
SRTO |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Pre-assessment notice, amount | $ 9.7 | ₩ 10.4 |  |  |

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