Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

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

Schedule of Stock-based Compensation Activity

The following is a summary of stock option activity for the three months ended March 31, 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	490		42.37
Exercised	(102	)	19.09
Canceled	(7	)	19.00
Outstanding at March 31, 2018	3,773		$	17.90

The following is a summary of restricted stock unit activity for the three months ended March 31, 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	(97	)	10.38
Canceled	—		—
Outstanding as of March 31, 2018	293		$	24.84

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 March 31,
	2018	2017
Risk free interest rate	2.3% to 2.7%	2.1% to 2.3%
Expected term	6.0 to 6.1 years	6.0 to 6.1 years
Expected volatility	84.2% to 85.2%	76.4% 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 March 31,
	2018		2017
Cost of contract manufacturing	$	—	$	77
Research and development	681		517
Selling, general and administrative	1,231		1,079
Total	$	1,912	$	1,673