Notes Payable (Narrative) (Details) - USD ($)
3 Months Ended 9 Months Ended
Jul. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Oxford Finance LLC and Silicon Valley Bank          
Debt Instrument [Line Items]          
Interest expense   $ 300,000 $ 200,000 $ 800,000 $ 200,000
Effective interest rate (in percentage)   11.72%   11.72%  
Notes Payable | Secured Debt | Oxford Finance LLC and Silicon Valley Bank          
Debt Instrument [Line Items]          
Debt instrument, maximum borrowing capacity $ 20,000,000        
Notes payable, gross 10,000,000 $ 10,000,000   $ 10,000,000  
Remaining borrowing capacity 10,000,000        
Proceeds from sale of equity $ 15,000,000        
Stated interest rate ( in percentage) 8.275%        
Periodic payment terms, balloon payment to be paid, percentage of funded borrowings (in percentage) 3.00%        
Proceeds from debt, net of issuance costs $ 9,700,000        
Notes Payable | Secured Debt | Oxford Finance LLC and Silicon Valley Bank | Minimum          
Debt Instrument [Line Items]          
Early extinguishment of debt, prepayment fee (in percentage) 1.00%        
Notes Payable | Secured Debt | Oxford Finance LLC and Silicon Valley Bank | Maximum          
Debt Instrument [Line Items]          
Early extinguishment of debt, prepayment fee (in percentage) 3.00%        
Notes Payable | Secured Debt | Oxford Finance LLC and Silicon Valley Bank | LIBOR          
Debt Instrument [Line Items]          
Basis spread on variable rate (in percentage) 8.085%        
Common stock warrants          
Debt Instrument [Line Items]          
Warrants issued (in shares) 97,680        
Exercise price of warrants (usd per share) $ 4.095        
Warrants outstanding   $ 300,000   $ 300,000