Warrants, stock-based compensation, stock options, restricted stock and restricted stock units - Stock-based award plans (Details) - shares	Jan. 01, 2020	Jun. 30, 2020	Dec. 31, 2019
2007 Plan
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Common stock available for future awards (in shares)		0
2017 Plan
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Shares authorized under the plan (in shares)		1,042,314
Shares available for grant under the plan (in shares)		802,365
Annual increase in the shares available for grant under the plan (as a percent of shares of common stock outstanding)		4.00%
Increase in the shares available for grant under the plan (in shares)	1,126,172
2017 ESPP
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Shares available for grant under the plan (in shares)		871,422
Annual increase in the shares available for grant under the plan (as a percent of shares of common stock outstanding)		1.00%
Increase in the shares available for grant under the plan (in shares)	281,543
Outstanding stock options
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Options outstanding (in shares)		2,744,441	2,507,062
Outstanding stock options | 2007 Plan
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Options outstanding (in shares)		1,100,607
Outstanding stock options | 2017 Plan
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Options outstanding (in shares)		1,643,834
Shares authorized under the plan (in shares)		2,490,290
Unvested restricted stock units | 2017 Plan
Warrants, stock-based compensation, stock options, restricted stock and restricted stock units
Options outstanding (in shares)		479,996