9. Warrants

In connection with certain of its redeemable convertible preferred stock issuances, convertible debt financings, and other financing arrangements the Company issued warrants for shares of its common stock and various issues of its redeemable convertible preferred stock. Such warrants related to its redeemable convertible preferred stock were recorded as liabilities as a result of non-standard anti-dilution and redemption rights of the underlying stock and were carried at their estimated fair value using the Monte Carlo valuation model. In connection with the Company’s IPO, the warrants were converted to common stock warrants with no anti-dilution features.  The Company revalued the warrants as of the offering date, recorded a gain on the liability through the Statements of Operations, and subsequently reclassified the warrant liability to additional paid-in-capital.

All common stock warrants outstanding convert on a one-to-one basis to common stock.  During the three months ended September 30, 2014, 16,206 common stock warrants were exercised via a net exercise into 15,987 shares of common stock.  

A summary of outstanding common stock warrants at September 30, 2014 is as follows:

A summary of outstanding warrants at December 31, 2013 is as follows:

The fair value of the preferred stock warrant liability was $0 and $260 at September 30, 2014 and December 31, 2013, respectively. During the three months ended September 30, 2014 and September 30, 2013, the Company recorded a gain of $0 and $41, respectively, and $36 and ($202), respectively for the nine months ended September 30, 2014 and September 30, 2013, on the change in fair value of the preferred stock warrants. The liability was reclassified to additional paid-in-capital as of February 20, 2014, and the warrants were converted to common stock warrants.