Convertible Preferred Stock	12 Months Ended
Convertible Preferred Stock	Dec. 31, 2017
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	Convertible Preferred Stock The Company entered into a preferred stock purchase agreement (“Preferred Stock Purchase Agreement”), with certain investors in May 2015 (the “Initial Closing”), under which the Company agreed to sell up to 45,223,970 shares of Series A-1 convertible preferred stock and 4,361,530 shares of Series A-2 convertible preferred stock. Additionally, at the Initial Closing, the Company concurrently issued 6,295,810 shares of Series A-1 convertible preferred stock for net proceeds of $24.8 million. The Preferred Stock Purchase Agreement provided that, upon Board of Directors approval, each investor would purchase its pro-rata portion of the shares to be issued in one or more additional Series A-1 closings, and in any Series A-2 closings. Further, the Company agreed to sell and issue said shares of Series A-1 convertible preferred stock on the same terms as the first tranche, and to issue said shares of Series A-2 convertible preferred stock on the terms included in the Preferred Stock Purchase Agreement. The second and third Series A-1 closings added further obligations for new investors to participate in the Series A-2 tranches. The Company did not separately account for tranche purchase rights described above as they were not freestanding from the associated shares of convertible preferred stock. In May 2015 (the “First Additional Closing”) the Company and the Series A convertible preferred stock shareholders amended the Preferred Stock Purchase Agreement pursuant to which the Company agreed to sell up to an additional 456,250 shares of Series A-1 convertible preferred stock. Additionally, at the First Additional Closing, the Company issued 3,481,250 shares of Series A-1 convertible preferred stock for net proceeds of $13.9 million and in July 2015 (“Second Additional Closing”), the Company issued an additional 2,420,830 shares of Series A-1 convertible preferred stock for net proceeds of $9.6 million. In January 2016 (the “Third Additional Closing”), the Company issued 500,000 shares of Series A-1 convertible preferred stock, for net proceeds of $2.0 million, and also issued 11,250,000 shares of Series A-1 convertible preferred stock (the “first Tranche Closing”), for net proceeds of $45.0 million. In June 2016 (the “Second Tranche Closing and Series A-2 Closing”), the Company issued 22,166,550 shares of Series A-1 convertible preferred stock and 4,361,530 shares of Series A-2 convertible preferred stock, for net proceeds of $88.7 million and $34.9 million, respectively. All of these shares were sold under the Preferred Stock Purchase Agreement. In June 2016 (the “First Series B-1 Closing”), the Company entered into a preferred stock purchase agreement (“Series B Preferred Stock Purchase Agreement”) with certain investors, under which the Company sold 7,646,240 shares of Series B-1 convertible preferred stock at a price of $16.00 per share for net proceeds of $122.2 million. In connection with this financing, the Company amended and restated its certificate of incorporation to increase the authorized shares of its common stock to 81,787,360 shares and the authorized shares of its preferred stock to 63,288,470 shares, each with a par value of $0.01 per share. The authorized preferred shares consisted of 46,114,433 designated as Series A-1 convertible preferred stock, 4,361,533 designated as Series A-2 convertible preferred stock, 8,125,000 designated Series B-1 convertible preferred stock and 4,687,500 designated Series B-2 convertible preferred stock. In August 2016, (the “Second Series B-1 Closing”), the Company sold 478,120 shares of Series B-1 convertible preferred stock at a price of $16.00 per share for net proceeds of $7.6 million. In November 2017, the Company sold 1,764,710 shares of Series B-2 convertible preferred stock at a price of $17.00 per share for net proceeds of $29.9 million. Prior to the conversion of the convertible preferred stock upon closing of the IPO, the rights, preferences and privileges of the convertible preferred stock were as follows: Dividend Rights The holders of preferred stock were entitled to receive dividends, if and when declared by the Board of Directors, at the rate of $0.08 per share per annum for Series A-1, $0.16 per share per annum for Series A-2, $0.32 per share per annum for Series B-1, and $0.34 per share per annum for Series B-2, from and after the date of issuance of such shares. As of December 31, 2016, and through the date of conversion, no such dividends were declared or accrued. Dividends on any other class of capital stock could not be paid unless the holders of the preferred stock first received, or simultaneously received, the preferred stock dividend. The holders of preferred stock also participated in dividends paid on common stock as if the shares of preferred stock had been converted into shares of common stock and were considered participating securities. Conversion Rights The holders of preferred stock had right to convert at any time into shares of common stock initially at a one-for-one ratio. All shares of the preferred stock would have been automatically converted into shares common stock (i) upon the consent of the holders of at least a majority of the outstanding preferred stock, or (ii) upon the closing of a firmly underwritten initial public offering of common stock at a price of at least $5.00 per share resulting in at least $50.0 million of gross proceeds. The conversion price for each series of preferred stock was subject to an adjustment in the event of stock split, combination, common stock dividend or distribution, reclassification, exchange, substitution, or reorganization. Liquidation Rights In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or a deemed liquidation event, the holders of shares of preferred stock then outstanding were entitled to be paid out of the assets of the Company available for distribution to its stockholders, before any payment could have been made to the holders of common stock, an amount per share equal to the greater of (i) the original issue price for the Series of preferred stock held plus any dividends accrued but unpaid, whether or not declared; or (ii) such amount per share as would have been paid if all shares of preferred stock had been converted to common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation event. If assets of the Company available were insufficient to pay holders of Preferred Stock the full amount they are entitled to, the holders of preferred stock would have shared ratably in any distribution of the assets available for distribution in proportion to the amounts due such holders. After the payment of all preferential amounts required to be paid to the holders of shares of preferred stock, the remaining assets of the Company would have been distributed among the holders of the shares of common stock, pro rata based on the number of shares held by each such holder. The Company classified its convertible preferred stock outside of stockholders’ deficit as certain change in control events are outside the Company’s control. Redemption Upon certain change in control events that were outside of the Company’s control, including liquidation, sale or transfer of control of the Company, holders of the convertible preferred stock could have caused its redemption. Shares of preferred stock could have been redeemed by the Company at the original issue price for each series of preferred stock plus any dividends accrued but unpaid, whether or not declared, in three annual installments, upon a written request from the holders of a majority of the then outstanding shares of preferred stock, which request could have been made at any time after the fifth anniversary of the Series B-1 original issue date (on or after June 22, 2021). On each of the three annual redemption dates the Company could have redeemed the number of outstanding shares of preferred stock determined by dividing the total number of outstanding shares of preferred stock by the number of remaining redemption dates. Voting Rights Each share of preferred stock had voting rights equal to the number of shares of common stock into which the preferred stock could have been converted immediately after the close of business on the record date. As long as certain investors in Series A convertible preferred stock held 100,000 or more shares of convertible preferred stock purchased pursuant to the Preferred Stock Purchase Agreement, they were entitled to elect individually one member of the Board totaling five Series A Directors. Series B convertible preferred stockholders were entitled to elect one member of the Board by majority vote of the Series B convertible preferred stockholders. Together, Series A and Series B convertible preferred stock investors were entitled to elect two additional members of the Board that were not otherwise an affiliate of the Company or of any investor. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 60,365,020 shares of common stock. As of December 31, 2019 and 2018, the Company did not have any convertible preferred stock issued or outstanding.