Convertible Promissory Notes, Related Parties	6 Months Ended
Jun. 30, 2018
Convertible Promissory Notes, Related Party [Abstract]
Convertible Promissory Notes, Related Party [Text Block]	NOTE 8. Convertible Promissory Notes, Related Parties On December 10, 2014, the Company entered into a note purchase agreement with certain existing preferred stockholders under which the Company issued convertible promissory notes during December 2014 for total proceeds of $18.4 million. On November 20, 2015, the Company entered into a second note purchase agreement with certain existing preferred stockholders under which the Company issued convertible promissory notes during November and December 2015 for total proceeds of $11.0 million. These notes were issued with the same terms as the notes issued in 2014. As the holders of the convertible promissory notes each have an equity ownership in the Company, the convertible promissory notes were considered to be a related‑party transaction. The convertible promissory notes bore interest at a rate of 8.0% per annum. The principal and accrued interest on the notes were automatically convertible, upon a future issuance of convertible preferred stock having total proceeds of at least $25.0 million, into that same stock at a conversion price equal to 90% of the price paid by other investors in the financing event. Upon a liquidation event, such as an acquisition or initial public offering, at the election of the majority of the noteholders in each issuance, the principal and accrued interest on the notes could either (i) be paid in full at the initial closing of the liquidation event, or (ii) automatically convert into the Company’s Series C convertible preferred stock at a conversion price based on a specified valuation. After two years, if the notes had not been converted, the holders of a majority of the principal amount had the option to require the entire principal balance and accrued interest to become due and payable. However, in December 2016, in conjunction with the loan agreement with Oxford Finance (see note 9), all of the holders of convertible promissory notes signed subordination agreements, under which they agreed not to demand or receive any payment until all amounts owed to Oxford Finance under the loan agreement were fully paid in cash, thus extending the due dates of the promissory notes potentially to January 2021. This change reflected a debt modification that was not considered substantially significant. Accordingly, the Company did not apply extinguishment accounting, but accounted for the modification on a prospective basis. The convertible promissory notes had redemption features that were determined to be a compound embedded derivative requiring bifurcation and separate accounting at estimated fair value. The estimated fair value of the embedded derivative upon issuance was a liability of $1.9 million for the notes issued in 2014 and $1.3 million for the notes issued in 2015. The estimated fair value of these derivative instruments was recognized as a debt discount and as an embedded derivative liability on the balance sheet upon issuance of the convertible promissory notes. The embedded derivative required periodic re‑measurements to fair value while the instruments were still outstanding (see Note 4). There was no beneficial conversion feature as the conversion feature value was accounted for in the embedded derivative. The Company estimated the fair value of the compound embedded derivative utilizing a Monte Carlo Simulation model. The inputs used to determine the estimated fair value of the embedded derivative instrument included the probability of an underlying event triggering the redemption event and its timing prior to the maturity date of the convertible promissory notes. The fair value measurement was based upon significant inputs not observable in the market, including a valuation of the Company performed by an independent third-party at each balance sheet date. By December 31, 2017, the embedded derivative had zero value because the Merger (see Note 1), which was considered 90% probable of occurring, would not have triggered redemption and, had the Merger not occurred, it was unlikely that the Company would have found an alternative source of financing on favorable terms, so there would have been zero redemption value. The embedded derivative was extinguished when the Merger occurred on February 13, 2018. The Company incurred total debt issuance costs of $20,000 in connection with the 2014 issuance and $7,000 in connection with the 2015 issuance. The debt issuance costs, which were recorded as an additional debt discount, were being amortized over the term of the notes. The Company’s accrued interest associated with the convertible promissory notes amounted to $6.3 million and the unamortized debt discount to $0.4 million as of December 31, 2017. On February 13, 2018, the balance of the convertible promissory notes was $35.6 million, comprising accrued interest associated with the convertible promissory notes amounted to $6.6 million plus principal of $29.4 million, offset by the unamortized debt discount to $0.4 million. On that date, in conjunction with the Merger, the convertible promissory notes were exchanged for 1,571,702 shares of the Company’s common stock which, based on the closing stock price of $9.05, had a value of $14.2 million. The difference of $21.4 million was recorded as a capital contribution.

Convertible Promissory Notes, Related Parties

6 Months Ended

Jun. 30, 2018

Convertible Promissory Notes, Related Party [Abstract]

Convertible Promissory Notes, Related Party [Text Block]

NOTE 8. Convertible Promissory Notes, Related Parties

On December 10, 2014, the Company entered into a note purchase agreement with certain existing preferred stockholders under which the Company issued convertible promissory notes during December 2014 for total proceeds of $18.4 million.

On November 20, 2015, the Company entered into a second note purchase agreement with certain existing preferred stockholders under which the Company issued convertible promissory notes during November and December 2015 for total proceeds of $11.0 million. These notes were issued with the same terms as the notes issued in 2014.

As the holders of the convertible promissory notes each have an equity ownership in the Company, the convertible promissory notes were considered to be a related‑party transaction.

The convertible promissory notes bore interest at a rate of 8.0% per annum. The principal and accrued interest on the notes were automatically convertible, upon a future issuance of convertible preferred stock having total proceeds of at least $25.0 million, into that same stock at a conversion price equal to 90% of the price paid by other investors in the financing event. Upon a liquidation event, such as an acquisition or initial public offering, at the election of the majority of the noteholders in each issuance, the principal and accrued interest on the notes could either (i) be paid in full at the initial closing of the liquidation event, or (ii) automatically convert into the Company’s Series C convertible preferred stock at a conversion price based on a specified valuation.

After two years, if the notes had not been converted, the holders of a majority of the principal amount had the option to require the entire principal balance and accrued interest to become due and payable. However, in December 2016, in conjunction with the loan agreement with Oxford Finance (see note 9), all of the holders of convertible promissory notes signed subordination agreements, under which they agreed not to demand or receive any payment until all amounts owed to Oxford Finance under the loan agreement were fully paid in cash, thus extending the due dates of the promissory notes potentially to January 2021. This change reflected a debt modification that was not considered substantially significant. Accordingly, the Company did not apply extinguishment accounting, but accounted for the modification on a prospective basis.

The convertible promissory notes had redemption features that were determined to be a compound embedded derivative requiring bifurcation and separate accounting at estimated fair value. The estimated fair value of the embedded derivative upon issuance was a liability of $1.9 million for the notes issued in 2014 and $1.3 million for the notes issued in 2015. The estimated fair value of these derivative instruments was recognized as a debt discount and as an embedded derivative liability on the balance sheet upon issuance of the convertible promissory notes. The embedded derivative required periodic re‑measurements to fair value while the instruments were still outstanding (see Note 4). There was no beneficial conversion feature as the conversion feature value was accounted for in the embedded derivative.

The Company estimated the fair value of the compound embedded derivative utilizing a Monte Carlo Simulation model. The inputs used to determine the estimated fair value of the embedded derivative instrument included the probability of an underlying event triggering the redemption event and its timing prior to the maturity date of the convertible promissory notes. The fair value measurement was based upon significant inputs not observable in the market, including a valuation of the Company performed by an independent third-party at each balance sheet date. By December 31, 2017, the embedded derivative had zero value because the Merger (see Note 1), which was considered 90% probable of occurring, would not have triggered redemption and, had the Merger not occurred, it was unlikely that the Company would have found an alternative source of financing on favorable terms, so there would have been zero redemption value. The embedded derivative was extinguished when the Merger occurred on February 13, 2018.

The Company incurred total debt issuance costs of $20,000 in connection with the 2014 issuance and $7,000 in connection with the 2015 issuance. The debt issuance costs, which were recorded as an additional debt discount, were being amortized over the term of the notes.

The Company’s accrued interest associated with the convertible promissory notes amounted to $6.3 million and the unamortized debt discount to $0.4 million as of December 31, 2017.

On February 13, 2018, the balance of the convertible promissory notes was $35.6 million, comprising accrued interest associated with the convertible promissory notes amounted to $6.6 million plus principal of $29.4 million, offset by the unamortized debt discount to $0.4 million. On that date, in conjunction with the Merger, the convertible promissory notes were exchanged for 1,571,702 shares of the Company’s common stock which, based on the closing stock price of $9.05, had a value of $14.2 million. The difference of $21.4 million was recorded as a capital contribution.