Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees

The fair value of stock options granted to employees during the three months ended March 31, 2018 and 2017 was estimated at the date of grant using the following assumptions:

	Three Months Ended March 31,
	2018	2017
Risk-free interest rate	2.3 – 2.7%		2.1	%
Expected dividend yield	0%	0%
Expected term	5.8 years	5.8 years
Expected volatility	62 – 63%	67 – 68%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense during the three months ended March 31, 2018 and 2017 as follows:

	Three Months Ended March 31,
(in thousands)	2018		2017
Employee awards:
Research and development expense	$	334	$	468
General and administrative expense		430		328
Total stock-based compensation expense	$	764	$	796

Summary of Stock Option Activity

The following table summarizes stock option activity during the three months ended March 31, 2018:

						Weighted-Average Remaining		Aggregate
(in thousands, except per share amounts)	Options			Weighted-Average Exercise Price		Contractual Term (in years)		Intrinsic Value
Outstanding at December 31, 2017		1,616		$	22.07		6.65	$	60,031
Granted		566		$	10.74
Exercised		—		$	—
Forfeited		(145	)	$	21.04
Outstanding at March 31, 2018		2,037		$	19.00		7.22	$	—
Vested and expected to vest at March 31, 2018		2,036		$	19.00		7.22	$	—
Exercisable at March 31, 2018		1,032		$	25.17		4.97	$	—