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Fair Value Measurements - Acquisition of CyDex (Details) - Cydex Pharmaceuticals, Inc - Contingent Consideration Classified as Equity | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Credit Derivatives [Line Items] |  |
Average probability of commercialization (as a percent) | 12.50% | 12.50%
Market price of risk | 0.029 | 0.029
Measurement Input, Price Volatility |  |
Credit Derivatives [Line Items] |  |
Revenue volatility (as a percent) | 0.25 | 0.25

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