Stockholders' Deficit Common Stock (Tables)

9 Months Ended

Sep. 30, 2019

The following table summarizes the Company’s stock option activity since December 31, 2018:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2018		7,561,719		$	12.26	$	7.23	$	4,958
Granted		2,346,350			5.90
Exercised		(90,125	)		1.61
Forfeited		(1,559,913	)		12.69
Outstanding as of September 30, 2019		8,258,031		$	10.49	$	7.21	$	4,230
Options vested and expected to vest as of September 30, 2019		8,258,031			10.49		7.21		4,230
Options exercisable as of September 30, 2019		4,641,642		$	12.49		5.94	$	4,028

Summary of Restricted Stock Unit Activity

The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2018:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2018		226,900		$	9.64
Granted		15,000			2.29
Forfeited		(22,500	)		8.77
Vested		(73,500	)		9.98
Unvested restricted stock units as of September 30, 2019		145,900		$	8.85

Summary of Stock Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options, restricted stock units and the Company’s Employee Stock Purchase Plan (“ESPP”) in the following expense categories of its condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Research and development expenses	$	1,033	$	2,246	$	3,574	$	6,436
General and administrative expenses		1,004		2,071		2,625		6,451
	$	2,037	$	4,317	$	6,199	$	12,887