Preferred Stock Warrants	12 Months Ended
Dec. 31, 2016
Text Block [Abstract]
Preferred Stock Warrants	8. Preferred Stock Warrants In connection with the Series B redeemable convertible preferred stock financing, the Company issued warrants to purchase 4,000,000 shares of Series B redeemable convertible preferred stock at an exercise price of $0.01 per share. These warrants would become exercisable only when certain milestones were met on programs begun as a result of collaborations entered into in 2011 and 2012. In particular, 50% of the warrants would become exercisable upon the Company publicly announcing its first Investigational New Drug (“IND”) candidate to the extent such IND candidate was the result of, or related to, the Company’s previous collaboration(s) with Ironwood Pharmaceuticals and/or Zealand Pharma A/S, and the balance would become exercisable upon the first dosing of a human patient in a clinical trial that was the result of, or related to, the Company’s previous collaboration(s) with Ironwood Pharmaceuticals and/or Zealand Pharma A/S. In August 2013, the initial closing date for the Series B financing, the Company issued 2,000,000 of the warrants (“First Tranche Warrants”). On August 15, 2014, in connection with the closing of the Series B second tranche financing, the Company issued the balance of the warrants (“Second Tranche Warrants”). The fair value of the warrants outstanding as of December 31, 2015 was remeasured at $480,000, determined using a one-step binomial lattice model in combination with the Option Pricing Model and the following assumptions: risk-free interest rate of 0.90%, expected life of 1.6 years and expected volatility of 57.0% and probability of exercisability of 95% and 0% for the first tranche and second tranche, respectively. In March 2016, the Company made a public announcement related to a preclinical candidate which triggered the achievement of the milestone and warrants to purchase 2,000,000 shares of Series B redeemable convertible preferred stock became exercisable as of that date. In April 2016, 1,999,998 shares of Series B redeemable convertible preferred stock were issued for cash proceeds of $20,000 in connection with the exercise of warrants. Immediately prior to the exercise of the warrants, the fair value of the warrants was remeasured at $1.0 million, determined using a hybrid method of the Option Pricing Model with a 67% weighted value per share and the probability-weighted expected return method (“PWERM”) with a 33% weighted value per share. The following assumptions were used in the Option Pricing Model: risk-free interest rate of 0.73%, expected life of 2.0 years and expected volatility of 52.0%. The PWERM method included probabilities of three IPO scenarios occurring in July 2016. The scenarios were weighted based on the Company’s estimate of each event occurring in deriving the estimated fair value. Upon the exercise of warrants, the redeemable convertible preferred stock warrant liability of $1.0 million was reclassified to redeemable convertible preferred stock. In May 2016, the remaining warrants for the purchase of 2,000,000 shares of Series B redeemable convertible preferred stock expired unexercised. The Company recorded a charge of $525,000 and $872,000 for the years ended December 31, 2016 and 2014, respectively, representing the increase in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations. The Company recorded a gain of $543,000 for the year ended December 31, 2015, representing the decrease in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations.

8. Preferred Stock Warrants

In connection with the Series B redeemable convertible preferred stock financing, the Company issued warrants to purchase 4,000,000 shares of Series B redeemable convertible preferred stock at an exercise price of $0.01 per share. These warrants would become exercisable only when certain milestones were met on programs begun as a result of collaborations entered into in 2011 and 2012. In particular, 50% of the warrants would become exercisable upon the Company publicly announcing its first Investigational New Drug (“IND”) candidate to the extent such IND candidate was the result of, or related to, the Company’s previous collaboration(s) with Ironwood Pharmaceuticals and/or Zealand Pharma A/S, and the balance would become exercisable upon the first dosing of a human patient in a clinical trial that was the result of, or related to, the Company’s previous collaboration(s) with Ironwood Pharmaceuticals and/or Zealand Pharma A/S. In August 2013, the initial closing date for the Series B financing, the Company issued 2,000,000 of the warrants (“First Tranche Warrants”). On August 15, 2014, in connection with the closing of the Series B second tranche financing, the Company issued the balance of the warrants (“Second Tranche Warrants”).

The fair value of the warrants outstanding as of December 31, 2015 was remeasured at $480,000, determined using a one-step binomial lattice model in combination with the Option Pricing Model and the following assumptions: risk-free interest rate of 0.90%, expected life of 1.6 years and expected volatility of 57.0% and probability of exercisability of 95% and 0% for the first tranche and second tranche, respectively.

In March 2016, the Company made a public announcement related to a preclinical candidate which triggered the achievement of the milestone and warrants to purchase 2,000,000 shares of Series B redeemable convertible preferred stock became exercisable as of that date. In April 2016, 1,999,998 shares of Series B redeemable convertible preferred stock were issued for cash proceeds of $20,000 in connection with the exercise of warrants. Immediately prior to the exercise of the warrants, the fair value of the warrants was remeasured at $1.0 million, determined using a hybrid method of the Option Pricing Model with a 67% weighted value per share and the probability-weighted expected return method (“PWERM”) with a 33% weighted value per share. The following assumptions were used in the Option Pricing Model: risk-free interest rate of 0.73%, expected life of 2.0 years and expected volatility of 52.0%. The PWERM method included probabilities of three IPO scenarios occurring in July 2016. The scenarios were weighted based on the Company’s estimate of each event occurring in deriving the estimated fair value. Upon the exercise of warrants, the redeemable convertible preferred stock warrant liability of $1.0 million was reclassified to redeemable convertible preferred stock.

In May 2016, the remaining warrants for the purchase of 2,000,000 shares of Series B redeemable convertible preferred stock expired unexercised.

The Company recorded a charge of $525,000 and $872,000 for the years ended December 31, 2016 and 2014, respectively, representing the increase in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations. The Company recorded a gain of $543,000 for the year ended December 31, 2015, representing the decrease in the fair value of the redeemable convertible preferred stock warrant liability in the consolidated statements of operations.