Capitalization	12 Months Ended
Dec. 31, 2017
Equity [Abstract]
Capitalization	Note 9—Capitalization In September 2016, and in preparation of the IPO and the establishment of two classes of common stock, each share of the then outstanding common stock was reclassified to Class B common stock. The Company sold Class A common stock in the IPO. The Class A and Class B have the same rights and preferences including rights to dividends, except the Class B is entitled to ten votes per share and the Class A is entitled to one vote per share. Each share of Class B common stock is convertible at any time at the option of the holder into one share of Class A common stock. In addition, each share of Class B common stock will convert automatically into one share of Class A common stock upon any transfer, except for certain transfers described in the Company’s restated certificate of incorporation, including, without limitation, certain transfers for tax and estate planning purposes. During the period from September 2016 through December 2016, 4.2 million shares of Class B common stock were converted to Class A common stock, and during the year ended December 31, 2017, 21.8 million shares of Class B common stock were converted to Class A common stock. In addition, upon the earlier of (1) the date on which the outstanding shares of Class B common stock represent less than 10% of the aggregate number of the then outstanding shares of Class A common stock and Class B common stock and (2) the affirmative vote or written consent of the holders of at least 66 2 ⁄ 3 % of the outstanding shares of Class B common stock, all outstanding shares of Class B common stock will convert automatically into Class A common stock, and no additional shares of Class B common stock will be issued. Prior to the reclassification of existing common stock to Class B common stock, the existing common stock was entitled to one vote per share. As of December 31, 2017, the Company is authorized to issue 1,095,000,000 shares of common stock, par value $0.000001 per share, and 100,000,000 shares of preferred stock, par value, $0.000001 per share. The authorized common stock consists of 1,000,000,000 shares of Class A common stock and 95,000,000 shares of Class B common stock. No shares of preferred stock are outstanding as of December 31, 2016 and 2017. The Company’s board of directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock. Initial Public Offering On September 26, 2016, the Company completed its IPO whereby 4,666,667 shares of Class A common stock were issued and sold by the Company and 700,000 shares of Class A common stock were sold by selling stockholders, pursuant to the underwriters’ exercise of their over-allotment option, at the IPO price of $18.00 per share. The Company received net proceeds from the offering of approximately $78.1 million after deducting underwriting discounts and commissions of $5.9 million, but before deducting offering costs of $4.5 million. The Company did not receive any proceeds from the sales of shares by the selling stockholders. In connection with the Company’s IPO: (1) all shares of the Company’s outstanding Series Seed, A-1, A-2, A-3, B and C convertible preferred stock automatically converted into an aggregate 22,078,637 shares of Class B common stock on a one for one-third basis and (2) warrants exercisable for 1,382,505 shares of convertible preferred stock were automatically converted into warrants exercisable for 460,834 shares of Class B common stock and net exercised resulting in the issuance of 448,545 shares of Class B common stock based on the IPO price of $18.00 per share and taking into account the 1-for-3 reverse stock split. In addition, upon completion of the IPO, costs associated with the IPO of $4.5 million were reclassified from other assets, non-current to additional paid-in capital. Secondary Offerings In March 2017, the Company completed a secondary offering (the “March 2017 Offering”) in which a total of 7,281,789 shares of Class A common stock were sold by certain selling stockholders to the public at a price of $35.50 per share, including 949,798 shares of Class A common stock sold to the underwriters pursuant to an option to purchase additional shares granted to them. In June 2017, the Company completed another secondary offering (the “June 2017 Offering”) in which a total of 4,846,600 shares of Class A common stock were sold by certain selling stockholders to the public at a price of $52.00 per share, including 530,148 shares of Class A common stock sold to the underwriters pursuant to an option to purchase additional shares granted to them. The Company did not receive any proceeds from either the March 2017 Offering or the June 2017 Offering. The Company incurred $0.9 million and $0.6 million in offering costs related to the March 2017 Offering and the June 2017 Offering, respectively, and these costs were included within general and administrative expenses in the condensed consolidated statements of operations during the first and second quarters of 2017, respectively. Convertible Preferred Stock In February 2016, the Company issued 11,500,587 shares of Series C convertible preferred stock for $60.0 million and used $54.0 million of the proceeds to repurchase 3,897,928 and 8,485,350 shares of Series Seed preferred stock (including shares issued upon exercise of warrant described below) and Series A preferred stock (comprising shares of Series A-1, A-2 and A-3), respectively, each at 80% of the Series C offering price per share of $5.22, and 188,786 shares of common stock at a price per share of $12.51. Warrants to purchase 808,135 shares of Seed preferred stock were net exercised, resulting in the issuance of 788,755 shares of Series Seed preferred stock of which 614,052 shares were then repurchased. The repurchase price of the convertible preferred stock, including legal costs, of $51.8 million exceeded the carrying value of $4.6 million at the date of repurchase. The repurchase price in excess of the then carrying value of the preferred stock of $47.2 million was recorded as a reduction to additional paid-in capital of $1.2 million and a reduction to retained earnings of $46.0 million. For the computation of net loss per share attributable to common stockholders for the year ended December 31, 2016, the repurchase price in excess of the then carrying value of the preferred stock of $47.2 million was recorded as a reduction to net income in computing net loss attributable to common stockholders. All shares of the Company’s outstanding Series Seed, A-1, A-2, A-3, B and C convertible preferred stock automatically converted into an aggregate 22,078,637 shares of Class B common stock on a one for one-third basis upon the completion of the Company’s IPO. Modification of Series B Preferred Stock In 2015, the Series B preferred stockholders agreed to modify the then liquidation rights and preference of the Series B preferred stock. The Company recorded the modification as an extinguishment as the fair value of the Series B preferred stock immediately before and immediately after the modification were substantially different (i.e., more than10%). The Company recorded the difference between the carrying value of the Series B preferred stock and the fair value after the modification, of $3.8 million, as a reduction to the carrying value of the Series B preferred stock and a reduction to accumulated deficit. The $3.8 million has been recorded as an adjustment to the net income attributable to common stockholders in accordance with ASC 260, Earnings per Share. Rights and Preferences of Convertible Preferred Stock Prior to the Company’s IPO, the Company’s convertible preferred stock had voting rights that allowed the holder to vote the number of common stock equal to which such shares of preferred stock could be converted; entitled the preferred stockholders to certain dividend right; entitled the holders to preference in payment upon a liquidation event, including upon a change in control, prior to the common stock holders equal to the greater of the original purchase price plus any dividends or such amount per share as would have been payable had all shares of the preferred stock been converted into common stock; and were convertible at the option of the holder at any time or automatically upon a qualified IPO.

Note 9—Capitalization

In September 2016, and in preparation of the IPO and the establishment of two classes of common stock, each share of the then outstanding common stock was reclassified to Class B common stock. The Company sold Class A common stock in the IPO. The Class A and Class B have the same rights and preferences including rights to dividends, except the Class B is entitled to ten votes per share and the Class A is entitled to one vote per share. Each share of Class B common stock is convertible at any time at the option of the holder into one share of Class A common stock. In addition, each share of Class B common stock will convert automatically into one share of Class A common stock upon any transfer, except for certain transfers described in the Company’s restated certificate of incorporation, including, without limitation, certain transfers for tax and estate planning purposes. During the period from September 2016 through December 2016, 4.2 million shares of Class B common stock were converted to Class A common stock, and during the year ended December 31, 2017, 21.8 million shares of Class B common stock were converted to Class A common stock. In addition, upon the earlier of (1) the date on which the outstanding shares of Class B common stock represent less than 10% of the aggregate number of the then outstanding shares of Class A common stock and Class B common stock and (2) the affirmative vote or written consent of the holders of at least 66 2 ⁄ 3 % of the outstanding shares of Class B common stock, all outstanding shares of Class B common stock will convert automatically into Class A common stock, and no additional shares of Class B common stock will be issued. Prior to the reclassification of existing common stock to Class B common stock, the existing common stock was entitled to one vote per share.

As of December 31, 2017, the Company is authorized to issue 1,095,000,000 shares of common stock, par value $0.000001 per share, and 100,000,000 shares of preferred stock, par value, $0.000001 per share. The authorized common stock consists of 1,000,000,000 shares of Class A common stock and 95,000,000 shares of Class B common stock.

No shares of preferred stock are outstanding as of December 31, 2016 and 2017. The Company’s board of directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock.

Initial Public Offering

On September 26, 2016, the Company completed its IPO whereby 4,666,667 shares of Class A common stock were issued and sold by the Company and 700,000 shares of Class A common stock were sold by selling stockholders, pursuant to the underwriters’ exercise of their over-allotment option, at the IPO price of $18.00 per share. The Company received net proceeds from the offering of approximately $78.1 million after deducting underwriting discounts and commissions of $5.9 million, but before deducting offering costs of $4.5 million. The Company did not receive any proceeds from the sales of shares by the selling stockholders. In connection with the Company’s IPO: (1) all shares of the Company’s outstanding Series Seed, A-1, A-2, A-3, B and C convertible preferred stock automatically converted into an aggregate 22,078,637 shares of Class B common stock on a one for one-third basis and (2) warrants exercisable for 1,382,505 shares of convertible preferred stock were automatically converted into warrants exercisable for 460,834 shares of Class B common stock and net exercised resulting in the issuance of 448,545 shares of Class B common stock based on the IPO price of $18.00 per share and taking into account the 1-for-3 reverse stock split.

In addition, upon completion of the IPO, costs associated with the IPO of $4.5 million were reclassified from other assets, non-current to additional paid-in capital.

Secondary Offerings

In March 2017, the Company completed a secondary offering (the “March 2017 Offering”) in which a total of 7,281,789 shares of Class A common stock were sold by certain selling stockholders to the public at a price of $35.50 per share, including 949,798 shares of Class A common stock sold to the underwriters pursuant to an option to purchase additional shares granted to them.

In June 2017, the Company completed another secondary offering (the “June 2017 Offering”) in which a total of 4,846,600 shares of Class A common stock were sold by certain selling stockholders to the public at a price of $52.00 per share, including 530,148 shares of Class A common stock sold to the underwriters pursuant to an option to purchase additional shares granted to them.

The Company did not receive any proceeds from either the March 2017 Offering or the June 2017 Offering. The Company incurred $0.9 million and $0.6 million in offering costs related to the March 2017 Offering and the June 2017 Offering, respectively, and these costs were included within general and administrative expenses in the condensed consolidated statements of operations during the first and second quarters of 2017, respectively.

Convertible Preferred Stock

In February 2016, the Company issued 11,500,587 shares of Series C convertible preferred stock for $60.0 million and used $54.0 million of the proceeds to repurchase 3,897,928 and 8,485,350 shares of Series Seed preferred stock (including shares issued upon exercise of warrant described below) and Series A preferred stock (comprising shares of Series A-1, A-2 and A-3), respectively, each at 80% of the Series C offering price per share of $5.22, and 188,786 shares of common stock at a price per share of $12.51. Warrants to purchase 808,135 shares of Seed preferred stock were net exercised, resulting in the issuance of 788,755 shares of Series Seed preferred stock of which 614,052 shares were then repurchased.

The repurchase price of the convertible preferred stock, including legal costs, of $51.8 million exceeded the carrying value of $4.6 million at the date of repurchase. The repurchase price in excess of the then carrying value of the preferred stock of $47.2 million was recorded as a reduction to additional paid-in capital of $1.2 million and a reduction to retained earnings of $46.0 million. For the computation of net loss per share attributable to common stockholders for the year ended December 31, 2016, the repurchase price in excess of the then carrying value of the preferred stock of $47.2 million was recorded as a reduction to net income in computing net loss attributable to common stockholders.

All shares of the Company’s outstanding Series Seed, A-1, A-2, A-3, B and C convertible preferred stock automatically converted into an aggregate 22,078,637 shares of Class B common stock on a one for one-third basis upon the completion of the Company’s IPO.

Modification of Series B Preferred Stock

In 2015, the Series B preferred stockholders agreed to modify the then liquidation rights and preference of the Series B preferred stock. The Company recorded the modification as an extinguishment as the fair value of the Series B preferred stock immediately before and immediately after the modification were substantially different (i.e., more than10%). The Company recorded the difference between the carrying value of the Series B preferred stock and the fair value after the modification, of $3.8 million, as a reduction to the carrying value of the Series B preferred stock and a reduction to accumulated deficit. The $3.8 million has been recorded as an adjustment to the net income attributable to common stockholders in accordance with ASC 260, Earnings per Share.

Rights and Preferences of Convertible Preferred Stock

Prior to the Company’s IPO, the Company’s convertible preferred stock had voting rights that allowed the holder to vote the number of common stock equal to which such shares of preferred stock could be converted; entitled the preferred stockholders to certain dividend right; entitled the holders to preference in payment upon a liquidation event, including upon a change in control, prior to the common stock holders equal to the greater of the original purchase price plus any dividends or such amount per share as would have been payable had all shares of the preferred stock been converted into common stock; and were convertible at the option of the holder at any time or automatically upon a qualified IPO.