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Fair Value Measurements - Quantitative Information used in Valuing Level 3 Liabilities (Details) - Discounted Cash Flow $ in Millions | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
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Contingent Payment Arrangements | Growth rates |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Contingent payment arrangements, measurement input | 0.07 | 0.07
Contingent Payment Arrangements | Growth rates | Weighted Average |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Contingent payment arrangements, measurement input | 0.07 | 0.07
Contingent Payment Arrangements | Discount rates |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Contingent payment arrangements, measurement input | 0.15 | 0.15
Contingent Payment Arrangements | Discount rates | Weighted Average |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Contingent payment arrangements, measurement input | 0.15 | 0.15
Affiliate Equity Repurchase Obligations | Growth rates | Minimum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | (0.04) | (0.04)
Affiliate Equity Repurchase Obligations | Growth rates | Maximum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.09 | 0.09
Affiliate Equity Repurchase Obligations | Growth rates | Weighted Average |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.05 | 0.03
Affiliate Equity Repurchase Obligations | Discount rates | Minimum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.13 | 0.14
Affiliate Equity Repurchase Obligations | Discount rates | Maximum |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.17 | 0.16
Affiliate Equity Repurchase Obligations | Discount rates | Weighted Average |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Affiliate equity repurchase obligations, measurement input | 0.15 | 0.15
Significant Unobservable Inputs (Level 3) | Contingent Payment Arrangements |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Fair value liabilities | $ 2.0 | $ 1.9
Significant Unobservable Inputs (Level 3) | Affiliate Equity Repurchase Obligations |  |
Quantitative information for Level 3 Fair Value Measurements Liabilities |  |
Fair value liabilities | $ 75.4 | $ 36.2

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