Stock Based Compensation - Summary of Stock Incentive Plans (Details) - USD ($)			12 Months Ended
	Jun. 16, 2020	May 12, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Stock Based Compensation
Option outstanding			4,456,748	3,902,675	4,456,748	3,902,675
Options available for grant under stock option plans			596,597	479,829	596,597	479,829
Shares Available for Grant
Beginning balance (in shares)			479,829
Ending balance (in shares)			596,597	479,829
Stock Options Outstanding
Beginning balance (in shares)			3,902,675
Options exercised (in shares)			(555)	0
Ending balance (in shares)			4,456,748	3,902,675
RSUs Outstanding
Beginning balance (in shares)			5,613
Ending balance (in shares)			5,613	5,613
Options vested, exercisable and expected to vest
Options exercised (in shares)			555	0
Weighted average grant date fair value of stock options granted (in dollars per share)			$ 0.40	$ 1.54
Number of options vested (in shares)			1,449,214	944,821
Common Stock, Capital Shares Reserved for Future Issuance					12,379,304	27,200,498
Weighted average fair value of options vested on grant date			$ 2.00	$ 3.12
Inducement options issued and outstanding
Stock Based Compensation
Option outstanding			114,892	74	114,892	74
Stock Options Outstanding
Beginning balance (in shares)			74
Ending balance (in shares)			114,892	74
Stock options and RSUs
Stock Based Compensation
Option outstanding			4,571,566	3,902,675	4,571,566	3,902,675
Options available for grant under stock option plans			596,597	479,829	596,597	479,829
Shares Available for Grant
Beginning balance (in shares)			479,829
Additional shares authorized (in shares)				786,229
Options granted (in shares)				(1,034,818)
Options cancelled (in shares)				365,357
Ending balance (in shares)			596,597	479,829
Stock Options Outstanding
Beginning balance (in shares)			3,902,675
Options granted (in shares)				1,034,818
Options exercised (in shares)			(555)
Options cancelled (in shares)				(365,357)
Options canceled not rolled back into the 2013 Plan (in shares)			(15)
Ending balance (in shares)			4,571,566	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)				$ 0.43
Options exercised (in dollars per share)			0.45
Options cancelled (in dollars per share)				3.81
Options canceled not rolled back into the 2013 Plan (in dollars per share)			2,661.75
Ending balance (in dollars per share)			$ 4.23	$ 5.20
Weighted Average Remaining Contractual Life (Years)
Weighted Average Remaining Contractual Life (Years)			8 years 8 months 16 days	9 years 6 months 22 days
Options vested, exercisable and expected to vest
Options vested and exercisable (in shares)					2,254,832
Options vested and exercisable (in dollars per share)					$ 7.12
Options vested and exercisable (in years)			8 years 6 months 26 days
Options vested and expected to vest (in shares)					4,285,311
Options vested and expected to vest (in dollars per share)					$ 4.43
Options vested and expected to vest (in years)			8 years 8 months 12 days
Options exercised (in shares)			555
Aggregate Intrinsic Value ,outstanding					$ 364
Aggregate Intrinsic Value, Exercisable					83,000
Aggregate Intrinsic Value, Vested and expected to vest					$ 320,000
2013 Plan
Stock Based Compensation
Option shares outstanding					384	395
2013 Plan | Stock options
Stock Options Outstanding
Options granted (in shares)			0
2014 Plan
Stock Based Compensation
Incentive stock option term		P10Y
Option outstanding			4,456,364	3,902,276	4,456,364	3,902,276
Options available for grant under stock option plans			211,415	479,829	211,415	479,829
Shares Available for Grant
Beginning balance (in shares)			479,829
Ending balance (in shares)			211,415	479,829
Stock Options Outstanding
Beginning balance (in shares)			3,902,276
Ending balance (in shares)			4,456,364	3,902,276
2014 Plan | Stock options
Stock Based Compensation
Increase in share reserve based on outstanding number of shares (as a percent)		2.00%
2020 New Employee Inducement Award Plan
Stock Based Compensation
Number of shares reserved for issuance	500,000
Incentive stock option term	P10Y
Option outstanding			114,818		114,818
Options available for grant under stock option plans			385,182		385,182
Shares Available for Grant
Ending balance (in shares)			385,182
Stock Options Outstanding
Ending balance (in shares)			114,818
Common Stock
Options vested, exercisable and expected to vest
Share Price					$ 0.815
Participants Voting Power More than Ten Percent | 2014 Plan
Stock Based Compensation
Incentive stock option term		P5Y
Participants Voting Power More than Ten Percent | 2020 New Employee Inducement Award Plan
Stock Based Compensation
Incentive stock option term	P5Y