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Organization and Significant Accounting Policies, Fair Value Measurements - Novartis Future Stock Purchase (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Mar. 31, 2017
Jan. 31, 2017
Novartis [Member]      
Novartis Future Stock Purchase [Abstract]      
Additional amount of common stock required to be purchased   $ 50,000 $ 50,000
Fair value of potential future premium     $ 5,000
Equity Securities [Member]      
Unobservable Inputs (Level 3) [Roll Forward]      
Beginning balance of Level 3 instruments $ 0    
Value of the potential premium we will receive from Novartis at inception of the SPA (January 2017) 5,035    
Write-off of premium to other expenses (5,035)    
Ending balance of Level 3 instruments $ 0