Stockholders' Equity	6 Months Ended
Jun. 30, 2018
Stockholders' Equity
Stockholders' Equity	5. Stockholders’ Equity Common Stock Each common stockholder is entitled to one vote for each share of common stock held. The common stock will vote together with all other classes and series of stock of the Company as a single class on all actions to be taken by the Company’s stockholders. Each share of common stock is entitled to receive dividends, as and when declared by the Company’s board of directors. The Company has never declared cash dividends on its common stock and does not expect to do so in the foreseeable future. June 2018 Registered Offering In June 2018, the Company entered into an underwriting agreement with Goldman Sachs & Co. LLC, as representative of the several underwriters named therein (the "June 2018 Underwriters"), relating to an underwritten public offering (the "June 2018 Offering") of 1,079,580 shares of the Company's common stock, including 95,973 shares of the Company's common stock purchased by the June 2018 Underwriters pursuant to a 30-day option to purchase such additional shares granted therein, at a public offering price of $305.00 per share. The June 2018 Offering resulted in net proceeds to the Company of approximately $311.8 million, after deducting the June 2018 Underwriters' discount and other offering costs. The June 2018 Offering closed on June 11, 2018. December 2017 Registered Offering In December 2017, the Company entered into an underwriting agreement with Goldman Sachs & Co. LLC, as representative of the several underwriters named therein (the " December 2017 Underwriters"), relating to an underwritten public offering (the "December 2017 Offering") of 1,731,929 shares of the Company's common stock, including 225,904 shares of the Company's common stock purchased by the December 2017 Underwriters pursuant to a 30-day option to purchase such additional shares granted therein, at a public offering price of $83.00 per share. The December 2017 Offering resulted in net proceeds to the Company of approximately $135.5 million, after deducting the December 2017 Underwriters' discount and other offering costs. The December 2017 Offering closed on December 21, 2017. June 2017 Private Placement Offering and its Series A Convertible Preferred Stock In June 2017, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement)” with a group of institutional accredited investors, who were existing, non-controlling stockholders of the Company, pursuant to which the Company sold securities to the Investors in a private placement transaction (the “June 2017 Offering”). Under the terms of the Purchase Agreement, the Company sold 328,300 shares of its common stock at a price of $15.23 per share, and 1,969,797 shares of its Series A Convertible Preferred Stock (the “Series A Preferred Stock”) at a price of $15.23 per share. The June 2017 Offering resulted in gross proceeds to the Company of approximately $35.0 million, and net proceeds to the Company of approximately $34.9 million. The June 2017 Offering closed on June 23, 2017. The Series A Preferred Stock has a par value of $0.0001 per share and is convertible into shares of the common stock at a one-to-one ratio, subject to adjustment as provided in the Purchase Agreement. The terms of the Series A Preferred Stock are set forth in the Certificate of Designation of Preferences, Rights and Limitations of Series A Convertible Preferred Stock, that the Company filed with the Secretary of State of the State of Delaware on June 21, 2017. Each share of the Series A Preferred Stock is convertible into shares of Common Stock at any time at the holder’s option. Upon any liquidation, dissolution or winding-up of the Company, whether voluntary or involuntary, after the satisfaction in full of the debts of the Company and the payment of any liquidation preference owed to the holders of shares of capital stock of the Company ranking prior to the Series A Preferred Stock upon liquidation, the holders of the Series A Preferred Stock shall participate pari passu with the holders of the Common Stock (on an as-if-converted-to-Common-Stock basis) in the net assets of the Company. Shares of the Series A Preferred Stock will generally have no voting rights, except as required by law. Shares of the Series A Preferred Stock will be entitled to receive dividends before shares of any other class or series of capital stock of the Company (other than dividends in the form of the Common Stock) equal to the dividend payable on each share of the Common Stock, on an as-converted basis. At-The-Market Issuance Sales Agreement In October 2015, the Company entered into an at-the-market issuance sales agreement (the "October 2015 Sales Agreement"), with Cowen and Company, LLC ("Cowen"), pursuant to which the Company may issue and sell shares of its common stock, having an aggregate offering price of up to $100 million, from time to time, at the Company's option, through Cowen as its sales agent. Sales of common stock through Cowen may be made by any method that is deemed an "at-the-market" offering as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, including by means of ordinary brokers' transactions at market prices, in block transactions or as otherwise agreed by the Company and Cowen. Subject to the terms and conditions of the October 2015 Sales Agreement, Cowen will use commercially reasonable efforts consistent with its normal trading and sales practices to sell the common stock based upon the Company's instructions (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company is not obligated to make any sales of its common stock under the October 2015 Sales Agreement. Any shares sold will be sold pursuant to an effective shelf registration statement on Form S-3 (file no. 333-206135). The Company will pay Cowen a commission of up to 3% of the gross proceeds. The October 2015 Sales Agreement may be terminated by the Company at any time upon 10 days' notice. As of June 30, 2018, 597,356 shares have been sold under the October 2015 Sales Agreement for an aggregate of approximately $9.6 million in gross proceeds. Net proceeds to the Company were approximately $9.4 million after deducting commissions and other transactions costs. Of those shares sold, none were sold in 2018, and 215,539 were sold in 2017. Approximately $90.4 million remained reserved under the Company's shelf registration statement and the applicable prospectus supplement for possible future issuance under the October 2015 Sales Agreement.

5. Stockholders’ Equity

Common Stock

Each common stockholder is entitled to one vote for each share of common stock held. The common stock will vote together with all other classes and series of stock of the Company as a single class on all actions to be taken by the Company’s stockholders. Each share of common stock is entitled to receive dividends, as and when declared by the Company’s board of directors.

The Company has never declared cash dividends on its common stock and does not expect to do so in the foreseeable future.

June 2018 Registered Offering

In June 2018, the Company entered into an underwriting agreement with Goldman Sachs & Co. LLC, as representative of the several underwriters named therein (the "June 2018 Underwriters"), relating to an underwritten public offering (the "June 2018 Offering") of 1,079,580 shares of the Company's common stock, including 95,973 shares of the Company's common stock purchased by the June 2018 Underwriters pursuant to a 30-day option to purchase such additional shares granted therein, at a public offering price of $305.00 per share. The June 2018 Offering resulted in net proceeds to the Company of approximately $311.8 million, after deducting the June 2018 Underwriters' discount and other offering costs. The June 2018 Offering closed on June 11, 2018.

December 2017 Registered Offering

In December 2017, the Company entered into an underwriting agreement with Goldman Sachs & Co. LLC, as representative of the several underwriters named therein (the " December 2017 Underwriters"), relating to an underwritten public offering (the "December 2017 Offering") of 1,731,929 shares of the Company's common stock, including 225,904 shares of the Company's common stock purchased by the December 2017 Underwriters pursuant to a 30-day option to purchase such additional shares granted therein, at a public offering price of $83.00 per share. The December 2017 Offering resulted in net proceeds to the Company of approximately $135.5 million, after deducting the December 2017 Underwriters' discount and other offering costs. The December 2017 Offering closed on December 21, 2017.

June 2017 Private Placement Offering and its Series A Convertible Preferred Stock

In June 2017, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement)” with a group of institutional accredited investors, who were existing, non-controlling stockholders of the Company, pursuant to which the Company sold securities to the Investors in a private placement transaction (the “June 2017 Offering”). Under the terms of the Purchase Agreement, the Company sold 328,300 shares of its common stock at a price of $15.23 per share, and 1,969,797 shares of its Series A Convertible Preferred Stock (the “Series A Preferred Stock”) at a price of $15.23 per share. The June 2017 Offering resulted in gross proceeds to the Company of approximately $35.0 million, and net proceeds to the Company of approximately $34.9 million. The June 2017 Offering closed on June 23, 2017.

The Series A Preferred Stock has a par value of $0.0001 per share and is convertible into shares of the common stock at a one-to-one ratio, subject to adjustment as provided in the Purchase Agreement. The terms of the Series A Preferred Stock are set forth in the Certificate of Designation of Preferences, Rights and Limitations of Series A Convertible Preferred Stock, that the Company filed with the Secretary of State of the State of Delaware on June 21, 2017. Each share of the Series A Preferred Stock is convertible into shares of Common Stock at any time at the holder’s option. Upon any liquidation, dissolution or winding-up of the Company, whether voluntary or involuntary, after the satisfaction in full of the debts of the Company and the payment of any liquidation preference owed to the holders of shares of capital stock of the Company ranking prior to the Series A Preferred Stock upon liquidation, the holders of the Series A Preferred Stock shall participate pari passu with the holders of the Common Stock (on an as-if-converted-to-Common-Stock basis) in the net assets of the Company. Shares of the Series A Preferred Stock will generally have no voting rights, except as required by law. Shares of the Series A Preferred Stock will be entitled to receive dividends before shares of any other class or series of capital stock of the Company (other than dividends in the form of the Common Stock) equal to the dividend payable on each share of the Common Stock, on an as-converted basis.

At-The-Market Issuance Sales Agreement

In October 2015, the Company entered into an at-the-market issuance sales agreement (the "October 2015 Sales Agreement"), with Cowen and Company, LLC ("Cowen"), pursuant to which the Company may issue and sell shares of its common stock, having an aggregate offering price of up to $100 million, from time to time, at the Company's option, through Cowen as its sales agent. Sales of common stock through Cowen may be made by any method that is deemed an "at-the-market" offering as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, including by means of ordinary brokers' transactions at market prices, in block transactions or as otherwise agreed by the Company and Cowen. Subject to the terms and conditions of the October 2015 Sales Agreement, Cowen will use commercially reasonable efforts consistent with its normal trading and sales practices to sell the common stock based upon the Company's instructions (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company is not obligated to make any sales of its common stock under the October 2015 Sales Agreement. Any shares sold will be sold pursuant to an effective shelf registration statement on Form S-3 (file no. 333-206135). The Company will pay Cowen a commission of up to 3% of the gross proceeds. The October 2015 Sales Agreement may be terminated by the Company at any time upon 10 days' notice.

As of June 30, 2018, 597,356 shares have been sold under the October 2015 Sales Agreement for an aggregate of approximately $9.6 million in gross proceeds. Net proceeds to the Company were approximately $9.4 million after deducting commissions and other transactions costs. Of those shares sold, none were sold in 2018, and 215,539 were sold in 2017. Approximately $90.4 million remained reserved under the Company's shelf registration statement and the applicable prospectus supplement for possible future issuance under the October 2015 Sales Agreement.