Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Outstanding Long Term Debt Carrying Amount and Estimated Fair Value (Details)

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Fair Value Measurements - Outstanding Long Term Debt Carrying Amount and Estimated Fair Value (Details) - Novartis Note [Member] - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Carrying Amount [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt $ 14,572 $ 14,572
Fair Value [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt $ 13,873 $ 14,178