Investments and Fair Value Instruments (Tables)

12 Months Ended

Dec. 31, 2021

Investments And Fair Value Instruments [Abstract]

Summary of Amortized Cost and Fair Value of Investment Securities Portfolio

(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Estimated Fair Value
December 31, 2021
Cash equivalents:
Money market funds	$	26,842	$	—	$	—	$	26,842
Total Assets at Fair Value	$	26,842	$	—	$	—	$	26,842

(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Estimated Fair Value
December 31, 2020
Cash equivalents:
Money market funds	$	12,082	$	—	$	—	$	12,082
Short-term investments:
Corporate securities		10,969		656		—		11,625
Total Assets at Fair Value	$	23,051	$	656	$	—	$	23,707

Summary of Fair Value of Investment Securities

The fair value of the investment securities at December 31, 2021 were as follows:

	Fair Value Measurements at December 31, 2021
(Dollars in thousands)	Level 1		Level 2		Level 3		Total
Assets at Fair Value
Cash equivalents:
Money market funds	$	26,842	$	—	$	—	$	26,842
Total Assets at Fair Value	$	26,842	$	—	$	—	$	26,842

The fair value of the investment securities at December 31, 2020 were as follows:

	Fair Value Measurements at December 31, 2020
(Dollars in thousands)	Level 1		Level 2		Level 3		Total
Assets at Fair Value
Cash equivalents:
Money market funds	$	12,082	$	—	$	—	$	12,082
Short-term investments:
Corporate securities		11,625		—		—		11,625
Total Assets at Fair Value	$	23,707	$	—	$	—	$	23,707

Summary of Warrant Liabilities Measured and Recorded on Recurring Basis using Black-Scholes Model

The warrant liabilities were measured and recorded on a recurring basis using the Black-Scholes Model with the following assumptions at December 31, 2021 and 2020:

	January 2021 Warrants					September 2019 Warrants						June 2019 Warrants						March 2018 Warrants
	December 31, 2021			December 31, 2020		December 31, 2021			December 31, 2020			December 31, 2021			December 31, 2020			December 31, 2021			December 31, 2020
Expected term (in years)		4.58			—		3.20			4.20			2.96			3.96			1.22			2.22
Expected volatility		129.8	%		—		109.7	%		135.0	%		110.8	%		135.0	%		86.0	%		130.0	%
Risk-free interest rate		1.2	%		—		0.9	%		0.3	%		0.8	%		0.3	%		0.5	%		0.1	%
Expected dividend yield		0	%		—		0	%		0	%		0	%		0	%		0	%		0	%

Summary of Changes in Fair Value and Other Adjustments of Liabilities

The following table sets forth the establishment of the Company’s Level 3 liabilities, as well as a summary of the changes in the fair value and other adjustments (in thousands):

(Dollars in thousands)	Common Stock Warrant Liability - March 2018 Purchase Agreement			Common Stock Warrant Liability - June 2018 Offering			Common Stock Warrant Liability - June 2019 Offering			Common Stock Warrant Liability - September 2019 Offering			Common Stock Warrant Liability - January 2021 Offering			Contingent Liabilities			Total
Balance as of December 31, 2019	$	4,579		$	5,444		$	1,993		$	2,920		$	—		$	2,000		$	16,936
Change in fair value and    other adjustments		(2,277	)		(1,426	)		(1,161	)		(1,706	)		—			—		$	(6,570	)
Exercise of warrants		(1,641	)		(4,018	)		—			—			—			—		$	(5,659	)
ISI acquisition contingent    consideration		—			—			—			—			—			280		$	280
Balance as of December 31, 2020	$	661		$	—		$	832		$	1,214		$	—		$	2,280		$	4,987
Initial recognition		—			—			—			—		$	9,631			—		$	9,631
Change in fair value and    other adjustments		(654	)		—			(662	)		(991	)		(6,638	)		(210	)	$	(9,155	)
Balance as of December 31, 2021	$	7		$	—		$	170		$	223		$	2,993		$	2,070		$	5,463