Common Stock - Schedule of Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	13,998,426	4,133,703
Unvested restricted stock
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	4,430	22,150
Restricted stock units
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	0	3,333
Options to purchase common stock
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	3,879,535	3,112,771
Common stock warrants
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)		926,840
Employee stock purchase plan
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	59,461	68,609
Common stock warrants
Common Stock Capital Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	10,055,000