Warrants (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Summary of Common Stock Warrants Outstanding

The following common stock warrants were outstanding at December 31, 2020:

	Number of Common Stock Warrants		Per Share Exercise Price		Issuance Date	Expiration Date
Replacement warrants		155	$	483.00	March 3, 2012	March 3, 2022
Issued with redeemable preferred stock*		1,420		3.50	August 16, 2017	August 16, 2022
Issued with common units in the 2018 Unit Offering		3,300		2.7568	October 2, 2018	October 2, 2023
Issued with common units in the 2018 Registered Direct Offering		92,300		5.40	October 10, 2018	October 10, 2023
Issued with common units in the 2019 Registered Direct Offering (see Note 10)		50,000		3.21	March 12, 2019	March 12, 2024
Issued with common units in the 2020 Public Offering (see Note 10)		1,630,436		0.0001	July 16, 2020		—
Total		1,777,611
*Liability classified warrants

The following common stock warrants were outstanding at December 31, 2019:

	Number of Common Stock Warrants		Per Share Exercise Price		Issuance Date	Expiration Date
Replacement warrants		155	$	483.00	March 3, 2012	March 3, 2022
Issued with redeemable preferred stock*		62		80.10	August 16, 2017	August 16, 2022
Issued with common units in 2018 Unit Offering		2,505,250		2.7568	October 2, 2018	October 2, 2023
Underwriter warrant issued in 2018 Unit Offering		196,650		6.25	October 2, 2018	September 28, 2021
Issued with common units in the 2018 Registered Direct Offering		4,629,630		5.40	October 10, 2018	October 10, 2023
Issued with common units in the 2019 Registered Direct Offering (see Note 10)		3,052,959		3.21	March 12, 2019	March 12, 2024
Total		10,384,706
*Liability classified warrants

Summary of Warrant Activity

A summary of warrant activity is as follows:

	Year Ended December 31,
	2020			2019
Warrants outstanding, beginning		10,384,706			7,344,297
Issuances		1,631,794			3,052,959
Exercises		(10,238,889	)		(12,550	)
Warrants outstanding, ending		1,777,611			10,384,706