Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

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 and nine months ended September 30, 2017 and 2016 was estimated at the date of grant using the following assumptions:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2017	2016	2017	2016
Risk-free interest rate	1.7 – 1.8%	1.1 – 1.4%	1.7 – 2.1%	1.1 – 1.5%
Expected dividend yield	0%	0%	0%	0%
Expected term	5.0 – 5.8 years	5.8 years	5.0 – 6.1 years	5.0 – 5.8 years
Expected volatility	64 – 66%	67%	64 – 68%	67 – 69%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense during the three and nine months ended September 30, 2017 and 2016 as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2017		2016		2017		2016
Employee awards:
Research and development expense	$	734	$	1,216	$	6,118	$	4,206
General and administrative expense		846		958		4,992		4,045
Total stock-based compensation expense	$	1,580	$	2,174	$	11,110	$	8,251

Summary of Stock Option Activity

The following table summarizes stock option activity during the nine months ended September 30, 2017:

						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, 2016		1,902		$	57.68		5.97	$	7,564
Granted		2,098		$	23.77
Exercised		(290	)	$	21.74
Forfeited		(1,886	)	$	59.37
Outstanding at September 30, 2017		1,824		$	22.65		6.21	$	1,187
Vested and expected to vest at September 30, 2017		1,822		$	22.64		6.21	$	1,187
Exercisable at September 30, 2017		1,159		$	26.71		4.34	$	969