Quarterly report pursuant to Section 13 or 15(d)

Description of Business - Additional Information (Details)

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Description of Business - Additional Information (Details) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2017
Dec. 31, 2016
 [1]
Jun. 30, 2016
Dec. 31, 2015
Description Of Business [Line Items]        
Accumulated deficit $ 1,204,084 $ 1,193,613    
Working capital 1,700      
Carrying value of the loan 27,861      
Cash and cash equivalents 12,465 $ 25,742 $ 33,854 $ 65,767
Novartis [Member] | Collaborative Arrangement [Member]        
Description Of Business [Line Items]        
Milestone received under the collaboration agreement $ 10,000      
[1] The condensed consolidated balance sheet as of December 31, 2016 has been derived from the audited consolidated financial statements as of that date included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016.