Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2021

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of option activity

The following summarizes all option activity under the 2007 Plan, 2014 Plan and Inducement Plan:

				Weighted		Weighted average
				average		remaining
	Option			exercise		contractual
	Shares			price		term (year)
Balances at December 31, 2019		1,880,846		$	7.42		5.48
Granted		600,000			3.58
Exercised		(9,817	)		2.89
Forfeited		(511,528	)		8.87
Balances at December 31, 2020		1,959,501		$	4.79		5.92
Exercised		(72,726	)		3.99
Forfeited		(182,812	)		5.49
Balances at December 31, 2021		1,703,963		$	4.75		5.41
Vested and expected to vest at December 31, 2021		1,703,963
Vested and exercisable at December 31, 2021		1,266,428					7.27

Summary of RSUs activity

Activity related to RSUs is set forth below:

				Weighted average
	Number			grant date
	of shares			fair value
Balances at December 31, 2019		2,232,956		$	11.99
Granted		3,070,430			4.77
Vested		(1,150,707	)		10.06
Forfeited		(1,058,889	)		7.82
Balances at December 31, 2020		3,093,790		$	6.97
Granted		1,636,969			7.06
Vested		(1,452,893	)		6.42
Forfeited		(478,314	)		2.31
Balances at December 31, 2021		2,799,552		$	8.11

Stock Option

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Schedule of Fair Value of Employee Stock Options Estimated Using Black-Scholes Option Valuation Model

The following table presents the weighted‑average assumptions used to estimate the fair value of options granted during the periods presented:

	Year Ended December 31,
Stock Options	2021	2020	2019
Expected term (in years)	—	6.50	—
Expected volatility	—	82.65%	—
Risk-free interest rate	—	0.27%	—
Dividend yield	—	—	—

Employee Stock Purchase Plan

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Schedule of Fair Value of Employee Stock Options Estimated Using Black-Scholes Option Valuation Model

The following table presents the weighted-average assumptions used to estimate the fair value of the stock purchase rights granted under the employee stock purchase plan:

	Year Ended December 31,
ESPP	2021					2020					2019
Expected term (in years)	0.50		to	2.00		0.50		to	2.00		0.50		to	2.00
Expected volatility	64	%	to	101	%	68	%	to	139	%	69	%	to	77	%
Risk-free interest rate	0.06	%	to	0.20	%	0.14	%	to	1.57	%	1.87	%	to	2.06	%
Dividend yield	—					—					—