License Agreements (Details)
12 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Jun. 30, 2006
Eisai
License Agreement
USD ($)
Dec. 31, 2014
Eisai
License Agreement
Dec. 31, 2014
Eisai
License Agreement
Minimum
USD ($)
Dec. 31, 2014
Eisai
License Agreement
Maximum
USD ($)
Dec. 31, 2014
Clinical Trial Services Agreement
Ipsen
USD ($)
Dec. 31, 2013
Clinical Trial Services Agreement
Ipsen
USD ($)
Dec. 31, 2012
Clinical Trial Services Agreement
Ipsen
USD ($)
Dec. 31, 2005
Clinical Trial Services Agreement
Ipsen
USD ($)
Dec. 31, 2014
Clinical Trial Services Agreement
Ipsen
Minimum
USD ($)
Dec. 31, 2014
Clinical Trial Services Agreement
Ipsen
Minimum
EUR (€)
Dec. 31, 2014
Clinical Trial Services Agreement
Ipsen
Maximum
USD ($)
Dec. 31, 2014
Clinical Trial Services Agreement
Ipsen
Maximum
EUR (€)
Dec. 31, 2014
Clinical Trial Services Agreement
Ipsen
Sublicense Agreement
Maximum
License Agreements                                
Nonrefundable, non-creditable payment                     $ 250,000          
Additional payments to be made upon achievement of certain development and commercialization milestones                       12,100,000 10,000,000 43,600,000 36,000,000  
Royalty rate (as a percent)               5.00%                
Period after the date of the first commercial sale of the product for license expiration         10 years             10 years 10 years     10 years
Amount recorded in research and development expense 45,719,000 60,536,000 54,961,000         500,000 200,000 700,000            
Initial license fee paid       500,000                        
Payments to be made upon achievement of certain clinical and regulatory milestones           $ 1,000,000 $ 20,000,000