Stockholder's Equity (Tables)

6 Months Ended

Jun. 30, 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, 2019		1,515,923		$	18.65
Options granted		438,328			5.53
Options cancelled		(97,382	)		96.15
Options exercised		(2,000	)		0.66
Balances, June 30, 2019		1,854,869		$	11.48		7.1	$	6,804
Outstanding and expected to vest as of June 30, 2019		1,821,599		$	11.55		7.1	$	6,796
Exercisable as of June 30, 2019		1,464,578		$	11.86		6.5	$	6,692

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:

	June 30,
	2019
Expected volatility		111.0	%
Risk-free interest rate		2.5	%
Dividend yield		0.0	%
Expected life (in years)		6.0