Capitalization	12 Months Ended
Dec. 31, 2017
Capitalization
Capitalization	7. Capitalization On February 1, 2016, the Company amended its certificate of incorporation to effect a stock split whereby each issued and outstanding share of common stock and Class B-1, B-2, C and D preferred stock was converted into 1.38 shares of common stock, Class B-1, B-2, C and D preferred stock, respectively. The par value per share was not adjusted as a result of this stock split. All share information presented in these consolidated financial statements and accompanying footnotes has been retroactively adjusted to reflect the increased number of shares resulting from this action. All classes of preferred stock were automatically converted into shares of the Company’s common stock upon the closing of the IPO. Class B‑1 and B‑2 Preferred Stock On January 30, 2014, the Company entered into a Convertible Note and Class B Stock Purchase Agreement (the “Class B Purchase Agreement”) with PBM Capital Investments, LLC (“PBM”). Under the Class B Purchase Agreement, the Company sold to PBM a $0.5 million convertible promissory note (the “Class B Note”) (see Note 9) and granted PBM an option (the “Class B Option”) to purchase 809,385 shares of Class B‑1 preferred stock at a purchase price of $2.47 per share and a warrant (the “Class B‑2 Warrant”) to purchase 130,623 shares of Class B‑2 preferred stock at $2.57 per share (the “Class B Stock Closing”). To exercise the Class B Option, PBM was required to provide written notice of its intent on or before February 28, 2014, after which date the Class B Option would terminate. After the Class B Stock Closing, the Company also agreed to sell and PBM agreed to purchase, on the same terms and conditions, 1,011,721 additional shares of Class B‑1 preferred stock (the “Class B‑1 Milestone Shares”) and a warrant to purchase 163,278 additional shares of Class B‑2 preferred stock (the “Milestone Warrant”) on the same terms and conditions. The Class B‑1 Milestone Shares and Milestone Warrant were issued to PBM on May 4, 2015 in exchange for $2.5 million of cash upon the achievement of the defined milestone. The Class B‑2 Warrant and the Milestone Warrant may be exercised by the holder, in whole or in part, upon the payment of the exercise price in cash. The Class B‑2 Warrant and the Milestone Warrant terminate upon the earliest to occur of (a) the 10-year anniversary of their issuance date or (b) a liquidation event, as defined therein. Class C Preferred Stock On August 11, 2014, the Company entered into a Class C Stock Purchase Agreement with certain investors. At closing, one of these investors purchased 504,478 shares of Class C preferred stock at a price of $3.96 per share. After the initial closing, the Company agreed to sell, and these investors each agreed to purchase, an aggregate of 551,472 additional shares of Class C preferred stock at a purchase price of $4.53 per share (the “Class C Milestone Shares”) upon certain conditions which were met in March 2015, resulting in the Class C Milestone Shares being purchased by these investors in exchange for an aggregate purchase price of $5.0 million in cash. Class D Preferred Stock Issuance On September 3, 2015, the Company entered into a Class D Stock Purchase Agreement with an investor pursuant to which the Company issued and sold an aggregate of 3,093,092 shares of Class D preferred stock at a price per share of $21.01 for an aggregate of $64.8 million, net of issuance costs. Common Stock Settlement and Issuance On December 29, 2017, the Company entered into a settlement agreement and release with a stockholder to whom the Company had issued a promissory note in 2012. Under the settlement agreement, the Company was obligated to issue 105,237 shares of common stock as of December 31, 2017 and recognized a non-cash expense of $11.6 million within general and administrative expense for the year ended December 31, 2017. The Company issued the shares in January 2018.

7. Capitalization

On February 1, 2016, the Company amended its certificate of incorporation to effect a stock split whereby each issued and outstanding share of common stock and Class B-1, B-2, C and D preferred stock was converted into 1.38 shares of common stock, Class B-1, B-2, C and D preferred stock, respectively. The par value per share was not adjusted as a result of this stock split. All share information presented in these consolidated financial statements and accompanying footnotes has been retroactively adjusted to reflect the increased number of shares resulting from this action. All classes of preferred stock were automatically converted into shares of the Company’s common stock upon the closing of the IPO.

Class B‑1 and B‑2 Preferred Stock

On January 30, 2014, the Company entered into a Convertible Note and Class B Stock Purchase Agreement (the “Class B Purchase Agreement”) with PBM Capital Investments, LLC (“PBM”). Under the Class B Purchase Agreement, the Company sold to PBM a $0.5 million convertible promissory note (the “Class B Note”) (see Note 9) and granted PBM an option (the “Class B Option”) to purchase 809,385 shares of Class B‑1 preferred stock at a purchase price of $2.47 per share and a warrant (the “Class B‑2 Warrant”) to purchase 130,623 shares of Class B‑2 preferred stock at $2.57 per share (the “Class B Stock Closing”). To exercise the Class B Option, PBM was required to provide written notice of its intent on or before February 28, 2014, after which date the Class B Option would terminate.

After the Class B Stock Closing, the Company also agreed to sell and PBM agreed to purchase, on the same terms and conditions, 1,011,721 additional shares of Class B‑1 preferred stock (the “Class B‑1 Milestone Shares”) and a warrant to purchase 163,278 additional shares of Class B‑2 preferred stock (the “Milestone Warrant”) on the same terms and conditions. The Class B‑1 Milestone Shares and Milestone Warrant were issued to PBM on May 4, 2015 in exchange for $2.5 million of cash upon the achievement of the defined milestone.

The Class B‑2 Warrant and the Milestone Warrant may be exercised by the holder, in whole or in part, upon the payment of the exercise price in cash. The Class B‑2 Warrant and the Milestone Warrant terminate upon the earliest to occur of (a) the 10-year anniversary of their issuance date or (b) a liquidation event, as defined therein.

Class C Preferred Stock

On August 11, 2014, the Company entered into a Class C Stock Purchase Agreement with certain investors.

At closing, one of these investors purchased 504,478 shares of Class C preferred stock at a price of $3.96 per share.

After the initial closing, the Company agreed to sell, and these investors each agreed to purchase, an aggregate of 551,472 additional shares of Class C preferred stock at a purchase price of $4.53 per share (the “Class C Milestone Shares”) upon certain conditions which were met in March 2015, resulting in the Class C Milestone Shares being purchased by these investors in exchange for an aggregate purchase price of $5.0 million in cash.

Class D Preferred Stock Issuance

On September 3, 2015, the Company entered into a Class D Stock Purchase Agreement with an investor pursuant to which the Company issued and sold an aggregate of 3,093,092 shares of Class D preferred stock at a price per share of $21.01 for an aggregate of $64.8 million, net of issuance costs.

Common Stock Settlement and Issuance

On December 29, 2017, the Company entered into a settlement agreement and release with a stockholder to whom the Company had issued a promissory note in 2012. Under the settlement agreement, the Company was obligated to issue 105,237 shares of common stock as of December 31, 2017 and recognized a non-cash expense of $11.6 million within general and administrative expense for the year ended December 31, 2017. The Company issued the shares in January 2018.