Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Stock Options Activity

The following table summarizes our stock option activity for 2019:

	Shares (in thousands)	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2018	3,744	$	20.69
Granted	1,247	$	48.88
Exercised	(647)	$	14.49
Canceled	(91)	$	35.17
Outstanding at December 31, 2019	4,253	$	29.59	6.8	$	96,524
Exercisable at December 31, 2019	2,556	$	21.24	5.6	79,083

Schedule of Restricted Stock Units Activity

The following table summarizes the Company’s restricted stock unit activity for 2019:

	Shares (in thousands)	Weighted Average Fair Value per RSU at Grant Date
Nonvested at December 31, 2018	289	$	25.56
Granted	235	50.46
Vested	(37)	43.10
Canceled	(48)	29.71
Nonvested at December 31, 2019	439	36.97

Assumptions used in the Black-Scholes Option-Pricing Model

A summary of the assumptions used to estimate the fair values of stock option grants for the years presented is as follows:

	Year Ended December 31,
	2019	2018	2017
Risk free interest rate	1.4% to 2.6%	2.3% to 3.0%	1.8% to 2.3%
Expected term	5.3 to 6.1 years	5.3 to 6.1 years	5.1 to 6.1 years
Expected volatility	73.5% to 82.3%	80.1% to 85.2%	75.1% to 85.8%
Expected dividend yield	—%	—%	—%
Weighted-average fair value of option on grant date	$32.64	$30.87	$7.43

Stock-Based Compensation Expense

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

	Year Ended December 31,
	2019		2018		2017
Cost of contract manufacturing	$	—	$	—	$	71
Research and development	8,293		6,317		1,933
Selling, general and administrative	12,954		9,175		4,151
Total	$	21,247	$	15,492	$	6,155