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Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value Measured On A Recurring Basis - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Financial Assets |  |  |  |  |
Cash equivalents |  | $ 33.3 |  | $ 40.4 |
Investments in marketable securities | [1] | 81.0 |  | 77.8 |
Foreign currency forward contracts |  | 1.2 | [2] | 0.2 | [1]
Financial Liabilities |  |  |  |  |
Contingent payment arrangements | [2] | 9.8 |  | 9.4 |
Affiliate equity obligations | [2] | 79.4 |  | 49.2 |
Foreign currency forward contracts | [2] | 1.3 |  | 0.6 |
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |  |
Financial Assets |  |  |  |  |
Cash equivalents |  | 33.3 |  | 40.4 |
Investments in marketable securities | [1] | 81.0 |  | 77.8 |
Foreign currency forward contracts |  | 0.0 | [2] | 0.0 | [1]
Financial Liabilities |  |  |  |  |
Contingent payment arrangements | [2] | 0.0 |  | 0.0 |
Affiliate equity obligations | [2] | 0.0 |  | 0.0 |
Foreign currency forward contracts | [2] | 0.0 |  | 0.0 |
Significant Other Observable Inputs (Level 2) |  |  |  |  |
Financial Assets |  |  |  |  |
Cash equivalents |  | 0.0 |  | 0.0 |
Investments in marketable securities | [1] | 0.0 |  | 0.0 |
Foreign currency forward contracts |  | 1.2 | [2] | 0.2 | [1]
Financial Liabilities |  |  |  |  |
Contingent payment arrangements | [2] | 0.0 |  | 0.0 |
Affiliate equity obligations | [2] | 0.0 |  | 0.0 |
Foreign currency forward contracts | [2] | 1.3 |  | 0.6 |
Significant Unobservable Inputs (Level 3) |  |  |  |  |
Financial Assets |  |  |  |  |
Cash equivalents |  | 0.0 |  | 0.0 |
Investments in marketable securities | [1] | 0.0 |  | 0.0 |
Foreign currency forward contracts |  | 0.0 | [2] | 0.0 | [1]
Financial Liabilities |  |  |  |  |
Contingent payment arrangements | [2] | 9.8 |  | 9.4 |
Affiliate equity obligations | [2] | 79.4 |  | 49.2 |
Foreign currency forward contracts | [2] | $ 0.0 |  | $ 0.0 |
[1] | Amounts are presented within Investments and other assets.
[2] | Amounts are presented within Other liabilities.

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