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
1 Months Ended
Mar. 31, 2016
Dec. 31, 2015
[1]
Description Of Business [Line Items]    
Accumulated deficit $ (1,148,448) $ (1,140,083)
Cash, cash equivalents and marketable securities $ 46,600  
Servier [Member]    
Description Of Business [Line Items]    
Collaboration agreement termination date Mar. 26, 2016  
[1] The condensed consolidated balance sheet as of December 31, 2015 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, 2015.