Stock-Based Awards (Tables)

6 Months Ended

Jun. 30, 2020

Stock-Based Awards

Assumptions used to determine fair value of stock options granted

	Six Months Ended
	June 30,
	2020		2019
Risk-free interest rate	0.87	%	2.53	%
Expected term (in years)	6.1		6.3
Expected volatility	85.19	%	101.70	%
Expected dividend yield	0	%	0	%

Summary of stock option activity

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number	Exercise		Contractual	Intrinsic
	of Shares	Price		Term	Value
				(in years)
Outstanding as of December 31, 2019	3,102,221	$	20.33	6.55	$	148
Granted	734,800		1.30
Exercised	—		—
Forfeited and cancelled	(557,222)		21.33
Outstanding as of June 30, 2020	3,279,799	$	15.90	6.99	$	316
Options vested and expected to vest as of June 30, 2020	3,279,799	$	15.90	6.99	$	316
Options exercisable as of June 30, 2020	1,897,671	$	19.16	5.79	$	79

Summary of restricted stock units activity

		Weighted
		Average
		Grant Date
	Number	Fair Value
	of Shares	Per Share
Outstanding as of December 31, 2019	3,592,915	$	4.62
Granted	998,385		1.26
Vested	(1,618,634)		3.09
Forfeited and cancelled	(444,265)		4.12
Outstanding as of June 30, 2020	2,528,401	$	4.36

Stock-based compensation expense

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Cost of revenue	$	252	$	223	$	512	$	429
Research and development		939		1,721		1,755		3,315
General and administrative		2,118		2,654		4,495		5,126
Total stock-based compensation expense	$	3,309	$	4,598	$	6,762	$	8,870