Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 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 nine months ended September 30, 2018 and 2017 was estimated at the date of grant using the following assumptions:

	Nine Months Ended September 30,
	2018	2017
Risk-free interest rate	2.3 – 2.9%	1.7 – 2.1%
Expected dividend yield	0%	0%
Expected term	5.3 – 5.8 years	5.0 – 6.1 years
Expected volatility	62 – 64%	64 – 68%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense during the three and nine months ended September 30, 2018 and 2017 as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2018		2017		2018		2017
Employee awards:
Research and development expense	$	256	$	734	$	870	$	6,118
General and administrative expense		526		846		1,456		4,992
Total stock-based compensation expense	$	782	$	1,580	$	2,326	$	11,110

Summary of Stock Option Activity

The following table summarizes stock option activity during the nine months ended September 30, 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		667		$	10.31
Exercised		—		$	—
Forfeited		(477	)	$	21.58
Outstanding at September 30, 2018		1,806		$	17.86		7.24	$	—
Vested and expected to vest at September 30, 2018		1,806		$	17.86		7.24	$	—
Exercisable at September 30, 2018		966		$	23.01		5.81	$	—