Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2016
Related Party Transactions
Related Party Transactions	14. Related Party Transactions The Company rented an office in Northville, Michigan from an LLC owned by two officers under short‑term agreements during the years ended December 31, 2016, 2015 and 2014. The original facility lease, as amended, was cancelled and replaced with a cancellable lease agreement in August 2016 for limited use of office space in the same Northville location. The new lease agreement became effective in August 2016 and expires in September 2017. Rent expense under the related party agreements was $21,000, $23,000 and $6,000 during the years ended December 31, 2016, 2015 and 2014, respectively. A prepaid rent balance related to the short‑term agreements amounted to zero and $3,000 as of December 31, 2016 and 2015, respectively. During the first quarter of 2015, the Company issued $2.0 million of additional Convertible Notes (the 2015 Notes) as part of the Convertible Notes described in Note 4 — Debt. The 2015 Notes included four notes in the aggregate of $0.3 million issued to investors who were related to one board member and three officers of the Company. On March 31, 2015, all of the Convertible Notes (including the 2015 Notes) were converted into 516,421 shares of Series A preferred stock. The conversion included a total of 68,649 shares of Series A preferred stock issued to two officers of the Company, and 63,967 shares of Series A preferred stock issued to investors related to one board member and three officers of the Company. During the third quarter of 2015, the Company issued $2.8 million of Interim Notes as described in Note 4 — Debt. Such Interim Notes included five notes issued to two officers and three board members (or entities they control) in the amount of $0.5 million. In addition, such Interim Notes included four notes to investors who were related to three of the Company’s officers and to one of the Company’s key employees in the amount of $0.3 million. In December 2015, the Company issued an additional $2.7 million of Interim Notes, as described in Note 4 — Debt, which included six notes issued to two officers and four board members in the amount of $0.6 million. The December 2015 Interim Note issuances also included five notes to investors who were related to three of the Company’s officers in the amount of $0.2 million. In February 2016, the Company issued an additional $0.2 million of Interim Notes, as described in Note 4 — Debt, which included two notes issued to two board members (or entities they control) in the amount of $81,000. The February 2016 Interim Note issuances also included a $20,000 note to an investor who is related to an officer of the Company. In April 2016, the Company issued an additional $5.0 million of Interim Notes, as described in Note 4 — Debt, which included two notes to investors who were related to two of the Company’s officers in the aggregate amount of $0.2 million. The April 2016 Interim Notes issuances also included three notes to investors who were related to three of the Company’s directors in the aggregate amount of $2.3 million. The IPO included 154,450 shares sold to 5 officers and 3 board members, totaling $1.5 million. In addition, 500,000 shares were sold to 1 investor who is related to 1 of the Company’s directors, totaling $5.0 million, and 47,000 shares totaling $0.5 million were sold to 14 investors who are related to 5 officers of the Company.