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Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value Measured On A Recurring Basis - USD ($) | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Financial Assets |  |  |  |
Cash equivalents |  | $ 48,100,000 |  | $ 40,400,000
Investments in marketable securities |  | 144,100,000 |  | 77,800,000
Derivative financial instruments | [1] | 1,000,000 |  | 200,000
Financial Liabilities |  |  |  |
Contingent payment arrangements |  | 4,300,000 | [2] | 9,400,000
Affiliate equity repurchase obligations |  | 28,700,000 | [2] | 49,200,000
Derivative financial instruments | [2] | 4,500,000 |  | 600,000
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |
Financial Assets |  |  |  |
Cash equivalents |  | 48,100,000 |  | 40,400,000
Investments in marketable securities |  | 144,100,000 |  | 77,800,000
Derivative financial instruments | [1] | 0 |  | 0.0
Financial Liabilities |  |  |  |
Contingent payment arrangements |  | 0 | [2] | 0
Affiliate equity repurchase obligations |  | 0 | [2] | 0
Derivative financial instruments | [2] | 0 |  | 0
Significant Other Observable Inputs (Level 2) |  |  |  |
Financial Assets |  |  |  |
Cash equivalents |  | 0 |  | 0
Investments in marketable securities |  | 0 |  | 0
Derivative financial instruments | [1] | 1,000,000 |  | 200,000
Financial Liabilities |  |  |  |
Contingent payment arrangements |  | 0 | [2] | 0
Affiliate equity repurchase obligations |  | 0 | [2] | 0
Derivative financial instruments | [2] | 4,500,000 |  | 600,000
Significant Unobservable Inputs (Level 3) |  |  |  |
Financial Assets |  |  |  |
Cash equivalents |  | 0 |  | 0
Investments in marketable securities |  | 0 |  | 0
Derivative financial instruments | [1] | 0 |  | 0
Financial Liabilities |  |  |  |
Contingent payment arrangements |  | 4,300,000 | [2] | 9,400,000
Affiliate equity repurchase obligations |  | 28,700,000 | [2] | 49,200,000
Derivative financial instruments | [2] | $ 0 |  | $ 0
[1] | Amounts are presented within Other investments and assets.
[2] | Amounts are presented within Other liabilities.

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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