Redeemable Convertible Preferred Stock	12 Months Ended
Dec. 31, 2017
Redeemable Convertible Preferred Stock Disclosure [Abstract]
Redeemable Convertible Preferred Stock [Text Block]	8. Redeemable convertible preferred stock In November 2015, upon the closing of the Company’s IPO, all issued and outstanding redeemable convertible preferred stock was automatically converted into 17,647,054 shares of common stock, see Note 2. The Company’s redeemable convertible preferred stock (“Preferred Stock”), has been classified as temporary equity on the accompanying balance sheets instead of in stockholders’ deficit in accordance with authoritative guidance for the classification and measurement of redeemable securities as the redeemable convertible preferred stock is redeemable at the option of the holder after the redemption date, February 2021. The Company has authorized preferred stock amounting to 5,000,000 shares as of December 31, 2017 and 2016. The authorized preferred stock was classified under stockholders’ equity at December 31, 2017. Series A Preferred Stock The Company issued 45,000,000 shares of Series A Preferred Stock during 2014 and 2015. These shares were issued at various closings in 2014 and 2015 for $1.00 per share. The shares were issued in exchange for cash proceeds of $42.0 million, net of issuance costs of $32.0 thousand, and the exchange of outstanding redeemable Convertible Notes, including accrued interest, of approximately $2.9 million. Tranche Rights Issued with Series A Preferred Stock Included in the terms of the January 2014 Series A Preferred Stock Purchase Agreement were certain rights (“Tranche Rights”), granted to the investors of Series A Preferred Stock purchased in January 2014, including the holders of the redeemable Convertible Notes who exchanged the redeemable Convertible Notes. The Tranche Rights obligated the investors in Series A Preferred Stock to purchase and the Company to sell an additional 18,500,000 shares of Series A Preferred Stock at $1.00 per share contingent upon successful near term in licensing and progress on initial experiments and research and development planning (“Tranche Right I”). In addition, the investors were obligated to purchase, and the Company was obligated to sell an additional 20,000,000 shares of Series A Preferred Stock upon the development of project engine and achievement of certain clinical milestones (“Tranche Right II”). In addition, the Tranche Rights allowed the investors the ability to purchase the additional shares at their option at any time. The Tranche Rights were transferrable by the investors, subject to approval by the Board. The Company has concluded the Tranche Rights meet the definition of a freestanding financial instrument, as the Tranche Rights were legally detachable and separately exercisable from the Series A Preferred Stock. Therefore, the Company allocated the proceeds between the Tranche Rights and the Series A Preferred Stock. As the Series A Preferred Stock was redeemable at the holder’s option, the Tranche Rights were classified as an asset or liability and were initially recorded at fair value. The Tranche Rights were measured at fair value at each reporting period. Since the Tranche Rights were subject to fair value accounting, the Company allocated the proceeds to the Tranche Rights based on the fair value at the date of issuance with the remaining proceeds being allocated to the Series A Preferred Stock. The estimated fair value of the Tranche Rights was determined using a probability weighted present value model that considers the probability of closing a tranche, the estimated future value of Series A Preferred Stock each closing, and the investment required at each closing. Future values were converted to present value using a discount rate appropriate for probability adjusted cash flows. Tranche Right I was initially recorded as an asset of $1.5 million as the purchase price of the additional shares was greater than the estimated value of the Series A Preferred Stock at the expected settlement date. The Company issued 18,500,000 additional shares under Tranche Right I, in three separate closings during the year ended December 31, 2014 with total proceeds of $18.5 million, net of issuance costs. Prior to each closing, any change in the value of Tranche Right I was recorded as other financing expense. The fair value of the portion of the Tranche Right I settled at each closing was reclassified to Series A Preferred Stock. Tranche Right II was initially recorded as a liability of $4.1 million as the purchase price of the additional shares was less than the estimated price of the Series A Preferred Stock at the expected settlement date. In February 2015, Tranche Right II was settled when the Company closed the final issuance of Series A Preferred Stock. The Company recognized expense of $9.8 million related to the mark to market of Tranche Right II during the year ended December 31, 2015, which was included in other financing expense. The fair value of the Tranche Right II settled at closing was reclassified to Series A Preferred Stock. The initial carrying amount of the Series A Preferred Stock issued upon the closing of Tranche Right II amounted to approximately $36.1 million which exceeded the redemption value, therefore the carrying value was not subsequently adjusted. However, the Company reflected accrued dividends of approximately $1.2 million related to this issuance in the net loss attributable to common stockholders for the year ended December 31, 2015. Series B Preferred Stock The Company issued 30,000,001 shares of Series B Preferred Stock during 2015. These shares were issued for $3.00 per share. This issuance resulted in cash proceeds of $89.8 million, net of issuance costs of $0.2 million. Additionally, a discount of $5.0 million was recorded against the proceeds as the amount paid by Sanofi Genzyme was in excess of fair value of the Series B Preferred Stock at issuance.

8. Redeemable convertible preferred stock

In November 2015, upon the closing of the Company’s IPO, all issued and outstanding redeemable convertible preferred stock was automatically converted into 17,647,054 shares of common stock, see Note 2.

The Company’s redeemable convertible preferred stock (“Preferred Stock”), has been classified as temporary equity on the accompanying balance sheets instead of in stockholders’ deficit in accordance with authoritative guidance for the classification and measurement of redeemable securities as the redeemable convertible preferred stock is redeemable at the option of the holder after the redemption date, February 2021.

The Company has authorized preferred stock amounting to 5,000,000 shares as of December 31, 2017 and 2016. The authorized preferred stock was classified under stockholders’ equity at December 31, 2017.

Series A Preferred Stock

The Company issued 45,000,000 shares of Series A Preferred Stock during 2014 and 2015. These shares were issued at various closings in 2014 and 2015 for $1.00 per share. The shares were issued in exchange for cash proceeds of $42.0 million, net of issuance costs of $32.0 thousand, and the exchange of outstanding redeemable Convertible Notes, including accrued interest, of approximately $2.9 million.

Tranche Rights Issued with Series A Preferred Stock

Included in the terms of the January 2014 Series A Preferred Stock Purchase Agreement were certain rights (“Tranche Rights”), granted to the investors of Series A Preferred Stock purchased in January 2014, including the holders of the redeemable Convertible Notes who exchanged the redeemable Convertible Notes. The Tranche Rights obligated the investors in Series A Preferred Stock to purchase and the Company to sell an additional 18,500,000 shares of Series A Preferred Stock at $1.00 per share contingent upon successful near term in licensing and progress on initial experiments and research and development planning (“Tranche Right I”). In addition, the investors were obligated to purchase, and the Company was obligated to sell an additional 20,000,000 shares of Series A Preferred Stock upon the development of project engine and achievement of certain clinical milestones (“Tranche Right II”). In addition, the Tranche Rights allowed the investors the ability to purchase the additional shares at their option at any time. The Tranche Rights were transferrable by the investors, subject to approval by the Board.

The Company has concluded the Tranche Rights meet the definition of a freestanding financial instrument, as the Tranche Rights were legally detachable and separately exercisable from the Series A Preferred Stock. Therefore, the Company allocated the proceeds between the Tranche Rights and the Series A Preferred Stock. As the Series A Preferred Stock was redeemable at the holder’s option, the Tranche Rights were classified as an asset or liability and were initially recorded at fair value. The Tranche Rights were measured at fair value at each reporting period. Since the Tranche Rights were subject to fair value accounting, the Company allocated the proceeds to the Tranche Rights based on the fair value at the date of issuance with the remaining proceeds being allocated to the Series A Preferred Stock. The estimated fair value of the Tranche Rights was determined using a probability weighted present value model that considers the probability of closing a tranche, the estimated future value of Series A Preferred Stock each closing, and the investment required at each closing. Future values were converted to present value using a discount rate appropriate for probability adjusted cash flows.

Tranche Right I was initially recorded as an asset of $1.5 million as the purchase price of the additional shares was greater than the estimated value of the Series A Preferred Stock at the expected settlement date. The Company issued 18,500,000 additional shares under Tranche Right I, in three separate closings during the year ended December 31, 2014 with total proceeds of $18.5 million, net of issuance costs. Prior to each closing, any change in the value of Tranche Right I was recorded as other financing expense. The fair value of the portion of the Tranche Right I settled at each closing was reclassified to Series A Preferred Stock. Tranche Right II was initially recorded as a liability of $4.1 million as the purchase price of the additional shares was less than the estimated price of the Series A Preferred Stock at the expected settlement date. In February 2015, Tranche Right II was settled when the Company closed the final issuance of Series A Preferred Stock. The Company recognized expense of $9.8 million related to the mark to market of Tranche Right II during the year ended December 31, 2015, which was included in other financing expense. The fair value of the Tranche Right II settled at closing was reclassified to Series A Preferred Stock. The initial carrying amount of the Series A Preferred Stock issued upon the closing of Tranche Right II amounted to approximately $36.1 million which exceeded the redemption value, therefore the carrying value was not subsequently adjusted. However, the Company reflected accrued dividends of approximately $1.2 million related to this issuance in the net loss attributable to common stockholders for the year ended December 31, 2015.

Series B Preferred Stock

The Company issued 30,000,001 shares of Series B Preferred Stock during 2015. These shares were issued for $3.00 per share. This issuance resulted in cash proceeds of $89.8 million, net of issuance costs of $0.2 million. Additionally, a discount of $5.0 million was recorded against the proceeds as the amount paid by Sanofi Genzyme was in excess of fair value of the Series B Preferred Stock at issuance.