Equity and Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Stockholders Equity [Abstract]

Weighted-Average Assumptions for Stock Options

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

Employee Stock Options:

	Six Months Ended June 30,
	2019			2018
Risk-free interest rate		2.5	%		2.8	%
Dividend yield		0.0	%		0.0	%
Volatility		76.3	%		77.7	%
Expected life	6.1 years			6.1 years

Board of Directors Stock Options:

	Six Months Ended June 30,
	2019			2018
Risk-free interest rate		1.9	%		2.9	%
Dividend yield		0.0	%		0.0	%
Volatility		74.3	%		78.2	%
Expected life	6.3 years			6.4 years

2017ESPP:

	Six Months Ended June 30,
	2019			2018
Risk-free interest rate		2.5	%		1.6	%
Dividend yield		0.0	%		0.0	%
Volatility		64.1	%		62.3	%
Expected life	6 months			6 months