Summary of Significant Accounting Policies - (Tables)

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Schedule of weighted-average assumptions used to estimate grant date fair value of stock options

The weighted-average assumptions used to estimate grant date fair value of stock options using the Black-Scholes option pricing model were as follows for the six month periods ended June 30, 2021 and 2020:

	Three Months Ended June 30,		Six Months Ended June 30,
	2021	2020	2021	2020
Expected common stock price volatility	113%	118%	113%	117%
Risk-free interest rate	0.89%-0.94%	0.26%-0.36%	0.31%-0.96%	0.26%-1.34%
Expected term of options (years)	5.2	4.5	5.1	4.5
Expected dividend yield	—	—	—	—