Long-term Debt (Tables)
12 Months Ended
Dec. 31, 2015
Summary of Estimated Fair Values of Outstanding Warrants Using Black-Scholes Option-Pricing Model

The fair value of the outstanding Hercules warrants as of the IPO closing date was $0.8 million and was determined using the Black-Scholes option-pricing model with the following assumptions:

 

     FEBRUARY 4,
2014
 

Stock price

   $ 32.66   

Expected option term (in years)

     3.0   

Expected volatility

     62

Risk-free interest rate

     0.7

Expected dividend yield

     0.0

Series C Warrants [Member]  
Summary of Estimated Fair Values of Outstanding Warrants Using Black-Scholes Option-Pricing Model

The estimated fair value of the outstanding Series C warrants at the IPO closing date and December 31, 2013 was $2.3 million and $0.4 million, respectively. The estimated fair values were determined using the Black-Scholes option-pricing model with the following assumptions:

 

     FEBRUARY 4,
2014
    DECEMBER 31,
2013
 

Stock price

   $ 32.66      $ 8.84   

Expected option term (in years)

     4.4        4.5   

Expected volatility

     65     64

Risk-free interest rate

     1.5     1.3

Expected dividend yield

     0.0     0.0