Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Summary of Series B Preferred Stock and Accretion of Dividends

The following table summarizes Series B convertible preferred stock and the accretion of dividend activity for the years ended December 31, 2021 and 2020 (in thousands):

	Year Ended December 31,
	2021		2020
Series B Convertible Preferred Stock :
Balance at beginning of period	$	22,969	$	21,875
Cumulative dividends on Series B convertible preferred stock		1,148		1,094
Balance at end of period	$	24,117	$	22,969
Number of Common Shares Issuable Upon Conversion :
Number of shares at beginning of period		5,742		5,469
Cumulative dividends on Series B convertible preferred stock		287		273
Number of shares at end of period		6,029		5,742

Summary of Outstanding Warrants Issued by Company

Below is the summary of outstanding warrants issued by the Company as of December 31, 2021:

Warrant Type	Number of Shares Issuable Upon Exercise		Weighted Average Exercise Price		Issue Date	Expiration Date
April 21 Funds Warrants		275,000		3.50	May 5, 2020	May 5, 2023

Summary of Common Stock Reserved for Future Issuance

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance as of December 31, 2021 was as follows:

Exercise of outstanding stock options, vesting of restricted stock units ("RSU"), vesting of performance stock    units ("PSU"), and issuance of RSUs vested but not released	1,471,899
Employee Stock Purchase Plan	293,888
Shares of common stock available for grant under the 2011 Plan	947,004
Warrants to purchase common stock	275,000
Shares of common stock issuable upon conversion of Series B convertible preferred stock	7,541,449
Total	10,529,240