Stockholder's Equity (Tables)

3 Months Ended

Mar. 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, 2019		1,515,923		$	18.65
Options granted		396,128			5.52
Options cancelled		(60,917	)		89.77
Balances, March 31, 2019		1,851,134		$	13.50		7.2	$	8,424
Outstanding and expected to vest as of March 31, 2019		1,816,265		$	13.60		7.2	$	8,380
Exercisable as of March 31, 2019		1,449,684		$	14.06		6.6	$	7,897

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:

	March 31,
	2019
Expected volatility		111.0	%
Risk-free interest rate		2.5	%
Dividend yield		0.0	%
Expected life (in years)		6.0