Subsequent Events (Details) (USD $)
0 Months Ended 12 Months Ended 1 Months Ended 0 Months Ended
Oct. 07, 2014
Jun. 25, 2014
Jun. 11, 2014
Dec. 31, 2014
Jun. 30, 2006
Mar. 09, 2015
Jan. 28, 2015
Subsequent Events              
Stock Issued During Period, Shares, New Issues 2,750,000   6,500,000        
Proceeds from Issuance of Common Stock $ 46,900,000     $ 103,804,000      
Proceeds from public offering and exercise of underwriters option 53,400,000 50,400,000          
License Agreement | Eisai              
Subsequent Events              
Initial license fee paid         500,000    
Common Stock              
Subsequent Events              
Stock Issued During Period, Shares, New Issues       10,141,268      
Subsequent Event | License Agreement | Eisai              
Subsequent Events              
Initial license fee paid           400,000  
Subsequent Event | Common Stock              
Subsequent Events              
Stock Issued During Period, Shares, New Issues net of underwriters options exercised             4,000,000
Shares Issued, Price Per Share             $ 36.75
Stock Issued During Period, Shares, New Issues             4,600,000
Proceeds from Issuance of Common Stock             137,800,000
Proceeds from public offering and exercise of underwriters option             $ 158,600,000
Subsequent Event | Common Stock | Underwriters              
Subsequent Events              
Stock Issued During Period, Shares, New Issues             600,000