Stock Incentive Plans - Summary of Stock Incentive Plans (Details) - USD ($)		6 Months Ended		12 Months Ended
	May 12, 2015	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jun. 30, 2020	Jun. 16, 2020	Dec. 31, 2019
Stock Based Compensation
Option outstanding		4,458,419		3,902,675	4,458,419		3,902,675
Shares available for grant		710,299		479,829	710,299		479,829
Shares Available for Grant
Beginning balance (in shares)		479,829
Ending balance (in shares)		710,299		479,829
Stock Options Outstanding
Beginning balance (in shares)		3,902,675
Options granted (in shares)		853,318
Options cancelled (in shares)		(297,559)
Options canceled not rolled back into the 2013 Plan (in shares)		(15)
Ending balance (in shares)		4,458,419		3,902,675
RSUs Outstanding
Beginning balance (in shares)		5,613
Ending balance (in shares)		5,613		5,613
Weighted Average Remaining Contractual Life (Years)
Weighted Average Remaining Contractual Life (Years)		9 years 1 month 13 days		9 years 6 months 22 days
Options vested, exercisable and expected to vest
Weighted average grant date fair value of stock options granted (in dollars per share)		$ 0.41	$ 17.05
Number of options vested (in shares)		702,364	10,598
Weighted average fair value of options vested on grant date		$ 2.21	$ 132.26
Common Stock, Capital Shares Reserved for Future Issuance					24,070,825		27,200,498
Aggregate Intrinsic Value ,outstanding					$ 31
Inducement options issued and outstanding
Stock Based Compensation
Option outstanding		3,392		74	3,392		74
Stock Options Outstanding
Beginning balance (in shares)		74
Ending balance (in shares)		3,392		74
2013 Plan | Stock options
Stock Based Compensation
Option shares outstanding					384
Stock Options Outstanding
Options granted (in shares)		0
2014 Plan
Stock Based Compensation
Option outstanding		4,455,101		3,902,675	4,455,101		3,902,675
Shares available for grant		479,829		479,829			479,829
Shares Available for Grant
Beginning balance (in shares)		479,829
Additional shares authorized (in shares)		786,229
Options granted (in shares)		(853,318)
Options cancelled (in shares)		297,559
Ending balance (in shares)				479,829
Stock Options Outstanding
Beginning balance (in shares)		3,902,675
Ending balance (in shares)		4,455,101		3,902,675
RSUs Outstanding
Beginning balance (in shares)		5,613
Ending balance (in shares)		5,613		5,613
Weighted Average Stock Option Exercise Price
Beginning balance (in dollars per share)		$ 5.20
Options granted (in dollars per share)		0.45
Options cancelled (in dollars per share)		3.75
Ending balance (in dollars per share)		$ 4.39		$ 5.20
Options vested, exercisable and expected to vest
Options vested and exercisable (in shares)					1,549,977
Options vested and exercisable (in dollars per share)					$ 9.31
Options vested and exercisable (in years)		8 years 10 months 6 days
Options vested and expected to vest (in shares)					4,030,402
Options vested and expected to vest (in dollars per share)					$ 4.71
Options vested and expected to vest (in years)		9 years 1 month 6 days
Options exercised (in shares)		0
Aggregate Intrinsic Value, Vested and expected to vest					$ 28
2014 Plan | Stock options
Stock Based Compensation
Increase in share reserve based on outstanding number of shares (as a percent)	2.00%
Option outstanding		4,455,101			4,455,101
Shares available for grant		213,617			213,617
Shares Available for Grant
Ending balance (in shares)		213,617
Stock Options Outstanding
Ending balance (in shares)		4,455,101
2020 New Employee Inducement Award Plan
Stock Based Compensation
Option outstanding		3,318			3,318
Shares available for grant		496,682			496,682
Shares Available for Grant
Ending balance (in shares)		496,682
Stock Options Outstanding
Ending balance (in shares)		3,318
Options vested, exercisable and expected to vest
Common Stock, Capital Shares Reserved for Future Issuance						500,000
Common Stock
Options vested, exercisable and expected to vest
Share Price					$ 0.485