Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Stock-based Compensation Activity

The following is a summary of restricted stock unit activity for the six months ended June 30, 2018 (in thousands, except per share data):

	Shares (in thousands)		Weighted- Average Fair Value per Share at Grant Date
Outstanding as of December 31, 2017	259		$	10.43
Granted	131		42.65
Vested	(98	)	10.74
Canceled	(2	)	42.65
Outstanding as of June 30, 2018	290		$	24.61

The following is a summary of stock option activity for the six months ended June 30, 2018 (in thousands, except per share data):

	Shares (in thousands)		Weighted- Average Exercise Price per Share
Outstanding at December 31, 2017	3,392		$	14.41
Granted	657		42.14
Exercised	(193	)	17.78
Canceled	(19	)	21.90
Outstanding at June 30, 2018	3,837		$	18.95

Assumptions used in the Black-Scholes Option-Pricing Model

The estimated grant date fair value of the stock options was estimated using the Black-Scholes option pricing model, based on the following assumptions:

	Three Months Ended June 30,		Six Months Ended June 30,
	2018	2017	2018	2017
Risk free interest rate	2.6% to 2.9%	1.9% to 2.0%	2.3% to 2.9%	1.9% to 2.3%
Expected term	5.3 to 6.1 years	5.1 to 6.1 years	5.3 to 6.1 years	5.1 to 6.1 years
Expected volatility	80.1% to 83.6%	76.0% to 76.3%	80.1% to 85.2%	76.0% to 76.6%
Expected dividend yield	—%	—%	—%	—%

Stock-Based Compensation Expense

The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations (in thousands):

	Three Months Ended June 30,					Six Months Ended June 30,
	2018		2017			2018		2017
Cost of contract manufacturing	$	—	$	(6	)	$	—	$	71
Research and development	1,062		502			1,743		1,019
Selling, general and administrative	1,997		635			3,228		1,714
Total	$	3,059	$	1,131		$	4,971	$	2,804