Stock Purchase Warrants

9 Months Ended

Sep. 30, 2019

Warrants and Rights Note Disclosure [Abstract]

Stock Purchase Warrants

Stock Purchase Warrants

The Company has historically issued warrants to purchase shares of the Company’s common stock in connection with certain of its common stock offerings. The fair value of the warrants as of December 31, 2018 were initially measured using the Black-Scholes valuation model.  Inherent in the Black-Scholes valuation model are assumptions related to expected stock-price volatility, expected life, risk-free interest rate and dividend yield. The Company estimates the volatility of its common stock-based on historical volatility that matches the expected remaining life of the warrants. The risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve on the grant date for a maturity similar to the expected remaining life of the warrants. The expected life of the warrants is assumed to be equivalent to their remaining contractual term. The dividend rate is based on the historical rate, which the Company anticipates remaining at zero.  

During the nine months ended September 30, 2019, the Company issued 19,808 shares of common stock upon the exercise of warrants with an exercise price of $4.27 per share. There are no outstanding warrants as of September 30, 2019.