Stockholders' Equity - Common Stock for Future Issuance (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	12,371,042	2,422,862
2016 Stock Plan
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	699,376	1,023,378
Warrants to Purchase Common Stock
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	10,000,000	0
Outstanding stock options
Class of Stock [Line Items]
Common stock shares reserved for future issuance (in shares)	1,671,666	1,399,484