8. Warrants

On August 27, 2014 and March 31, 2015, the Company issued the 2014 Warrants and 2015 Warrants to purchase an aggregate 315,688 shares of series B convertible preferred stock at an exercise price of $0.9503 per share to the lenders in connection with the Credit Facility (Note 7). The 2014 Warrants and 2015 Warrants were exercisable upon issuance and have a seven-year life. The 2014 Warrants and 2015 Warrants were recorded as a liability and re-measured at each reporting date using the then-current assumptions. In connection with the completion of the IPO, the 2014 Warrants and the 2015 Warrants were automatically converted into warrants exercisable for 24,566 shares of Common Stock with an exercise price of $12.21 per share, resulting in the reclassification of the related warrant liability to additional paid-in capital as the warrants to purchase shares of Common Stock met the criteria to be accounted for as equity-classified instruments. The warrant liability was re-measured to fair value immediately prior to reclassification to additional paid-in capital. As of December 31, 2015, the Company had no outstanding warrant liability.

The following table provides a roll-forward of the fair value of the 2014 Warrants and 2015 Warrants determined by Level 3 inputs (in thousands):

	Fair Value
Balance at December 31, 2014	$	108
Issuance of warrants at fair value		107
Change in fair value, recorded as a component of the other (expense) income, net		(9	)
Reclassification to additional paid-in capital		(206	)

Balance at December 31, 2015	$	—

The fair value of warrants exercisable for 315,688 shares of series B convertible preferred stock was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions:

	June 30, 2015(1)			December 31, 2014
Risk-free interest rate		1.97	%		1.95	%
Expected dividend yield		0.00	%		0.00	%
Expected term (in years)		6.5			6.7
Expected volatility		75.79	%		78.16	%


(1)	Represents the date the warrants for series B convertible preferred stock converted to warrants for common stock

At various dates from 2008 through 2010, the Company issued warrants to purchase an aggregate of 34,839 shares of Common Stock at an exercise price of $1.67 per share to various individuals, including its founders and employees of the Company. The warrants have six-year terms.