Stock Based Awards (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

Activity under the Company’s stock option plans is set forth below:

						Weighted
						Average
				Weighted		Remaining		Aggregate
				Average		Contractual		Intrinsic
	Number of			Exercise		Life		Value
	Shares			Price		(in years)		(in thousands)
Balances, January 1, 2018		607,511		$	81.60
Additional shares authorized		—			—
Assumption of option plans associated with the merger		1,183,950			0.44
Options granted		—			—
Restricted stock units granted		—			—
Options exercised		(3,643	)		9.66
Options cancelled		(271,895	)		80.09
Balances, December 31, 2018		1,515,923			18.65
Additional shares authorized		—			—
Options granted		483,328			5.55
Restricted stock units granted		—			—
Options exercised		(39,686	)		2.40
Options cancelled		(139,405	)		81.33
Balances, December 31, 2019		1,820,160		$	10.70		6.6	$	18,957
Vested and expected to vest as of December 31, 2019		1,796,997		$	10.75		6.6	$	18,778
Exercisable as of December 31, 2019		1,474,782		$	11.31		6.0	$	16,311

Stock Options Outstanding and Exercisable under Stock Option Plans

The following table summarizes information with respect to stock options outstanding and currently exercisable and vested as of December 31, 2019:

					Options Exercisable
	Options Outstanding				and Vested
			Weighted Average				Weighted Average
			Remaining				Remaining
Range of	Number		Contractual		Number		Contractual
Exercise Prices	Outstanding		Life (in Years)		Outstanding		Life (in Years)
$0.06-$0.06		86,867		1.5		86,867		1.5
$0.24-$0.24		621,098		5.4		621,098		5.4
$0.66-$0.90		451,632		7.8		451,632		7.8
$3.54-$5.83		385,673		8.8		110,828		8.8
$5.87-$191.76		274,890		5.8		204,357		5.8
		1,820,160				1,474,782

Summary of Fair Value of Employee Stock Options

The fair value of employee stock options was estimated using the Black-Scholes model with the following weighted-average assumptions:

	Year Ended December 31,
	2019			2018
Expected volatility		111.0	%		132.0	%
Risk-free interest rate		2.4	%		3.0	%
Dividend yield		0.0	%		0.0	%
Expected life (in years)		6.0			3.3

Schedule of Estimated Stock-Based Compensation Expense

Stock-based compensation expense, net of estimated forfeitures, is reflected in the statements of operations as follows (in thousands):

	Year Ended December 31,
	2019		2018
Operating Expenses
Research and development	$	347	$	2,946
General and administrative		3,052		13,193
Total	$	3,399	$	16,139

Summary of Restricted Stock Activity

A summary of the Company’s restricted stock activity is presented in the following tables:

				Weighted
				Average
	Number of			Grant Date
	Shares			Fair Value
Restricted Stock Units
Unvested at December 31, 2018		117,597		$	31.37
Granted		—			—
Vested		(59,567	)		31.37
Forfeited/canceled		(15,918	)		27.16
Unvested at December 31, 2019		42,112		$	32.97