Stock-Based Compensation (Tables)

12 Months Ended

Dec. 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 years ended December 31, 2018 and 2017 was estimated at the date of grant using the following assumptions:

	Years Ended December 31,
	2018	2017
Risk-free interest rate	2.3 – 2.9%	1.7 – 2.2%
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 years ended December 31, 2018 and 2017 as follows:

	Years Ended December 31,
(in thousands)	2018		2017
Employee awards:
Research and development expense	$	1,092	$	6,902
General and administrative expense		1,958		5,886
Total stock-based compensation expense	$	3,050	$	12,788

Summary of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2018:

(in thousands, except per share amounts)	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2017		1,616		$	22.07		6.65	$	60,031
Granted		1,190		$	7.60
Exercised		—		$	—
Forfeited		(573	)	$	19.72
Outstanding at December 31, 2018		2,233		$	14.97		7.66	$	—
Vested and expected to vest at December 31,    2018		2,233		$	14.97		7.66	$	—
Exercisable at December 31, 2018		1,049		$	22.10		5.77	$	—