Liquidity (Details) - USD ($)
$ in Thousands
1 Months Ended
Feb. 28, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Liquidity [Line Items]          
Cash and cash equivalents   $ 6,260 $ 16,815 $ 0 $ 0
Marketable securities   17,807 $ 0    
Net proceeds to the company $ 51,900        
Underwriting discounts and commissions deducted 4,200        
Offering costs deducted $ 3,900        
Drug supply agreement | Affiliated Entity          
Liquidity [Line Items]          
Prepaid research and development   11,300      
Committed Equity Funding          
Liquidity [Line Items]          
Common stock, value, subscriptions   $ 20,000      
Commitment letter maximum ownership percentage (more than)   19.90%      
Committed Equity Funding First Two Draw Downs [Member]          
Liquidity [Line Items]          
Common stock, value, subscriptions   $ 2,000