Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 six months ended June 30, 2018 and 2017 were estimated at the date of grant using the following assumptions:

	Six Months Ended June 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	5.7 – 6.1 years
Expected volatility	62 – 63%	65 – 68%

Schedule of Recognized Stock-Based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2018		2017		2018		2017
Employee awards:
Research and development expense	$	280	$	4,916	$	614	$	5,383
General and administrative expense		500		3,818		930		4,146
Total stock-based compensation expense	$	780	$	8,734	$	1,544	$	9,529

Summary of Stock Option Activity

The following table summarizes stock option activity during the six months ended June 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		625		$	10.64
Exercised		—		$	—
Forfeited		(298	)	$	22.04
Outstanding at June 30, 2018		1,943		$	18.40		6.98	$	—
Vested and expected to vest at June 30, 2018		1,943		$	18.40		6.98	$	—
Exercisable at June 30, 2018		1,028		$	23.81		4.92	$	—