Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Stockholders Equity [Abstract]

Weighted-Average Assumptions for Stock Options

For the nine months ended September 30, 2019 and 2018, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

	Nine Months Ended September 30,
	2019			2018
Risk-free interest rate		2.3	%		2.7	%
Dividend yield		0.0	%		0.0	%
Volatility		75.6	%		77.1	%
Expected life	6.1 years			6.1 years

Board of Directors Stock Options:

	Nine Months Ended September 30,
	2019			2018
Risk-free interest rate		1.8	%		2.9	%
Dividend yield		0.0	%		0.0	%
Volatility		73.8	%		78.2	%
Expected life	6.3 years			6.4 years

2017ESPP:

	Nine Months Ended September 30,
	2019			2018
Risk-free interest rate		2.4	%		1.9	%
Dividend yield		0.0	%		0.0	%
Volatility		60.0	%		64.2	%
Expected life	6 months			6 months

Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense for the three and nine months ended September 30, 2019 and 2018 (in thousands):

	Three Months Ended September 30,					Nine Months Ended September 30,
	2019			2018		2019		2018
Cost of sales - product	$	127		$	—	$	382	$	—
Research and development expenses		2,814			2,313		9,298		6,868
Selling, general and administrative expenses		(6,405	)		10,417		19,779		24,371
Total	$	(3,464	)	$	12,730	$	29,459	$	31,239